Particle detectors

ABSTRACT

A beam detector including a light source, a receiver, and a target, acting in cooperation to detect particles in a monitored area. The target reflects incident light, resulting in reflected light being returned to receiver. The receiver is capable of recording and reporting light intensity at a plurality of points across its field of view. In the preferred form the detector emits a first light beam in a first wavelength band; a second light beam in a second wavelength band; and a third light beam in a third wavelength band, wherein the first and second wavelengths bands are substantially equal and are different to the third wavelength band.

PRIORITY CLAIM TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 14/451,330, filedAug. 4, 2014, which is a divisional application of U.S. Ser. No.13/318,309, filed Oct. 31, 2011, issued as U.S. Pat. No. 8,797,531,which is a U.S. national stage application filed under 35 U.S.C. §371from International Application No. PCT/AU2010/000511, filed May 3, 2010,and published as WO 2010/124347 A1 on Nov. 4, 2010, which claimspriority to Australian Application No. 2009901922, filed May 1, 2009,Australian Application No. 2009901923, filed May 1, 2009, AustralianApplication No. 2009901924, filed May 1, 2009, Australian ApplicationNo. 2009901925, filed May 1, 2009, Australian Application No.2009901926, filed May 1, 2009, and Australian Application No.2009901927, filed May 1, 2009, which applications and publication areincorporated by reference as if reproduced herein and made a part hereofin their entirety, and the benefit of priority of each of which isclaimed herein.

FIELD OF THE INVENTION

The present invention relates to aspects of particle detectors. By wayof example the embodiments will be described in relation to beamdetectors adapted for detecting smoke. In one aspect the presentinvention relates more generally to battery powered devices, althoughthe illustrative embodiment will be described in connection with beamdetectors.

BACKGROUND OF THE INVENTION

Various methods of detecting particles in air are known. One methodinvolves projecting a beam across a monitored area and measuring theattenuation of the beam. Such detectors are commonly known as‘obscuration detectors’, or simply ‘beam detectors’.

Some beam detectors employ a co-located transmitter and receiver with adistant reflector, and others use a separate transmitter unit andreceive a unit located on opposite sides of the open space beingmonitored.

An exemplary, conventional beam detector is shown in FIG. 1. Thedetector 10 includes a light source and detector 12 and a reflector 14placed either side of a monitored area 16. Incident light 18 from thelight source and detector 12 are projected toward the reflector 14. Thereflector 14 reflects the incident light 18 as reflected light 20 backtoward the light source and detector 12. If particulate matter entersthe monitored area 16, it will attenuate the incident light 18 andreflected light 20 and cause the amount of light received at the lightsource and detector 12 to diminish. An alternative beam detectorseparates the light source from the detector and omits the reflector anddirectly illuminates the detector with the light source across themonitored area 16. Other geometries are also possible.

Whilst the mechanism of smoke detection used by beam detectors is sound,beam detectors commonly suffer from a number of problems.

Firstly, beam detectors may suffer a type I (false positive) error whereforeign objects or other particulate matter, such as dust, enters themonitored area and obscure the beam. Beam detectors are generally unableto distinguish between the obscuration caused by particles of intereste.g. smoke, and obscuration which results from the presence of foreignbody of no interest e.g. a bug flying into the beam.

Secondly, beam detectors may require careful alignment at the time ofinstallation. Such alignment aims to ensure that in normal conditions,free from particles, light enters the sensor so as to capture themajority of the transmitted beam, and to in turn maximise sensitivity toan obscuration. This calibration may be slow and therefore costly toperform. Moreover, it may need to be repeated as the physicalenvironment changes, for example because of small movements in thestructure to which a beam detector is attached. In some cases, if theintensity of incident light on the detector diminishes quickly thismisalignment may also cause a false alarm.

The inventors have proposed a system to address some of these drawbacksin Australian provisional patent application 2008902909, filed 10 Jun.2008 in the name of Xtralis Technologies Ltd and International Patentapplication PCT/AU 2009/000727. An exemplary embodiment describedtherein and reproduced as FIG. 2 herein includes a light source 32, areceiver 34, and a target 36, acting in cooperation to detect particlesin a monitored area 38. The target 36, e.g. a corner cube reflectsincident light 40, resulting in reflected light 32 being returned toreceiver 34. In the preferred embodiment the receiver 34 is preferably avideo camera or other receiver having an array of light sensors e.g. oneor more CCD (charge-coupled device) image sensors, or CMOS(complementary metal-oxide-semiconductor) image sensors, or indeed anydevice capable of recording and reporting light intensity at a pluralityof points across its field of view.

In this system the receiver 34 receives all of the light in its field ofview 40, and includes imaging optics to form an image of a field of itsview 40, including the target 36 on its image sensor. Receiver 34records the intensity of light in its field of view, in the form of datarepresenting the image intensity at a series of locations throughout thefield of view. A portion of this data will correspond, at leastpartially, to reflected light 42. A microcontroller 54 analyses theimage data, and determines which portion of the data provides the bestestimate of reflected light 42. Because the receiver 34 has a wide fieldof view and has the ability to independently measure light at a widerange of points within this field of view the light source 32 need notbe carefully aligned with target 36, or with receiver 34, since theeffect of a misalignment will simply be that a different portion ofdata, corresponding to different pixels within the view, will be used tomeasure the reflected light 42. Accordingly, provided that the field ofview of the receiver includes target 36, one or more regions of interestwithin the image will include a measured value for the reflected light42.

If smoke or other particulate matter enters monitored area 38, it willobscure or scatter incident light 40 or reflected light 42. Thisobscuration or scattering will be detected as a drop in the intensityfor received reflected light 42 measured in the image region determinedby the microcontroller.

Pixels falling outside the region selected by the microcontroller, toinclude the reflected light 42, can be ignored as light received bythese pixels does not correspond to the reflected light 42.

Over time, as the building moves or other factors alter the geometry ofthe system, the target 36 will still be in the field of view of thereceiver 34 however, the image of the target 36 will appear at adifferent point on the image detector of the receiver 34. In order toaddress this motion, the microcontroller can be adapted to track theimage of the target 36 across its light sensor over time to enable asmoke detection to be performed on the correct image regions over time.

In some embodiments described therein the target 36 is illuminated attwo (or more) wavelengths λ₁ and λ₂ e.g. an infrared (IR) andultraviolet (UV) wavelength which are emitted by corresponding lightsources (or a common source) along two substantially collinear paths.

The wavelengths are chosen such that they display different behaviour inthe presence of particles to be detected, e.g. smoke particles. In thisway the relative change in the received light at the two (or more)wavelengths can be used to give an indication of what has causedattenuation of the beam.

Furthermore, the applicants earlier application depicts an embodimentcapable of monitoring multiple targets simultaneously. According to thisembodiment, illustrated in FIG. 3 herein, the detector 50 includes alight source 52, a receiver 54, a first target 56, and a second target57 acting in co-operation to detect smoke in monitored area 58. Target56 reflects incident light 62, resulting in reflected light 64 returningto receiver 54. Target 57 reflects incident light 65, resulting inreflected light 67 returning to receiver 54. As with the previousembodiment, the receiver 54 communicates the image data to amicrocontroller 74. Microcontroller 74 analyses the data, and determineswhich portion of the data contains information most strongly related toreflected light 64 and reflected light 67 respectively. At theconclusion of this decision process, the microcontroller 74 will haveselected two portions of data, corresponding to respective individualpixels or respective groups of pixels read from its image sensor, thatcan most reliably be used to measure the intensity of reflected light 64and reflected light 67 respectively. In this way the system 50 can, bythe addition of only an additional target or light source, perform thefunction of two beam detectors.

Using such a system, present inventors have previously proposed aparticle detection system which addresses the seemingly contradictoryrequirements of the need for high sensitivity and the need for a wideangular range of operation in a beam detection system. However, theseconstraints as well as constraints on the intensity of light sourcesable to be used as transmitters mean that there may be a need to furtherenhance the particle detection system in these respects.

In beam detectors the transmitted light intensity may be limited. Forexample, there may be budgetary considerations which mean that arelatively low power light emitter must be selected in the product.Furthermore, in some cases, a limited electrical power supply isavailable, especially if the transmitter unit is powered by a battery.Eye safety is also a factor in limiting the transmission power of thelight source as is the potential nuisance effect of visible light fromthe transmitter. For any of these reasons, a relatively low transmittedsignal power may be used in a beam detector. Consequently, the signal tonoise ratio of the system may be compromised.

In order to operate satisfactorily whilst keeping the emitted power aslow as possible it is advantageous, for sensitivity purposes, that thepolar emission pattern of the transmitter and the viewing angle of thereceiver are kept as narrow as possible. However, for installation andalignment purposes it is advantageous that the same angles are kept asbroad as possible. Accordingly, accommodating these seeminglycontradictory requirements of the system can present problems.

A further problem that may arise in such a system is that a reflectivesurface may provide one or more unintended light paths between thetransmitter and the receiver, and so interfere with either therecognition of the direct light path, or cause uncontrolled andunintended contributions to the received signal(s), or both. This effectis exacerbated if the reflective surface is subject to any changes, suchas movement with temperature or building wind loads; or the movement ofpeople or vehicles that causes its reflected contribution to vary overtime.

Since beam detector components are often mounted just below asubstantially flat ceiling, this type of undesired reflection may becommon. It has been realised by the inventors that to cause such anissue, the finish of the reflective surface does not need to beobviously reflective or mirror-like, and that even a common matt-paintedsurface may provide a relatively strong specular reflection at thenarrow angle of incidence, such as would typically occur in a beamdetector with a long span mounted near a surface. While a mirror like,or gloss finish is the extreme case, even an apparently rough surfacemay give enough specular reflection to create these problems.

Adjacent walls, particularly glazed walls, may also create a similarissue with the additional complication that blinds or open-able windowsmay be used at various times. However, this issue does not arise ascommonly, since it is rarely required that beams are directed in closeproximity to walls.

For this reason and others, beam detectors typically require carefulalignment at the time of installation. Such alignment aims to ensurethat in normal conditions, free from particles, light enters the sensorso as to capture the majority of the transmitted beam, and to in turnmaximise sensitivity to an obscuration. This calibration may be slow andtherefore costly to perform. Moreover, it may need to be repeated as thephysical environment changes, for example because of small movements inthe structure to which a beam detector is attached. In some cases, ifthe intensity of incident light on the detector diminishes quickly thismisalignment may also cause a false alarm.

Since beam detectors are typically mounted to a wall or like flatsurface it is generally not possible to get behind the detector in orderto use a line of sight type alignment device. Also, since detectors areusually mounted at high elevations and in inaccessible locations, theproblem of achieving accurate alignment, and the difficulties caused bymisalignment, are exacerbated.

As discussed in relation to FIG. 1, some beam detectors employ aco-located transmitter and receiver with a remote reflector. Anotherarrangement, as illustrated in FIG. 9, uses a light source 1102 that isremote from the receiver 1104. The separate transmitter 1102 may bebattery powered in order to avoid the requirement for costly wiring.Furthermore, in embodiments that are powered from the fire alarm loopthe detector unit 1104 (Or the combined light source and detector 102,of FIG. 1,) may also employ a battery to act as a reserve supply forperiods of high power consumption that exceed a specified limit ofcapacity of a wired loop supply.

In order to achieve the required service life, and for conformance withsafety requirements, it is desirable that the battery-powered unitsshould not be powered on during shipping or in long-term storage.

Conventionally, battery-powered equipment is often activated using amanual switch, or by removal of an insulating separator, or by insertingthe batteries into the equipment. The inventors have identified thatthese methods have several disadvantages, particularly in the case ofbeam-detection systems. The conventional systems for powering up thebattery-powered equipment are not automatic and, in consequence, may beoverlooked when the beam-detection system is installed. Inbeam-detection systems the wavelengths used for the light source 102,202 are often invisible to the human eye. This makes it difficult toconfirm that the light source 102, 202 is active when installed. Inaddition, the beam detection systems are often installed at asignificant height, requiring scaffolding or a cherry-picker to accessthe system components. As a result, it is time-consuming and costly toaccess and rectify a unit that has inadvertently been leftnon-operational.

Some of the conventional techniques of activating battery-powered unitsalso interfere with the common requirement that beam-detection systemsshould avoid arrangements that cause penetrations through the mainenclosure of the unit. It is often the case that transmitters aredesigned to be resistant to the entry of dust and moisture, and the useof manually-operated switches may makes this isolation more difficultand costly to achieve.

A further problem that may arise with beam detectors is that theirexposed optical surfaces may become contaminated with dirt over time.This can gradually reduce the received signal with the potential to beraise a false alarm. Methods to avoid and remove dirt build up onoptical surfaces are known, and employed particularly commonly in thefield of closed circuit TV security surveillance applications, such asthe use of contamination-resistant coatings on viewing windows,protective shrouds, wash-wipe mechanisms and the like.

Also, as described in PCT/AU2008/001697 in the name of XtralisTechnologies Limited, there are other mechanical means for cleaning oravoiding dirt build up on optical surfaces, including methods usingfiltered clean air as a barrier, or electrostatic guard areas to preventwindow contamination. Such methods may advantageously be used for beamdetectors separately or in combination with other aspects of the currentinvention, and each constitute an aspect of the present invention.

With the dual wavelength system described in connection with FIGS. 2 and3 a variation in the absolute intensities of received light is toleratedto an extent, because a differential measure is used to detect particlesin the beam, but relative variation between the wavelengths may createfaults or, worse still, false alarms; specifically a relative reductionin the received signal from the UV beam compared to the IR beam may bemistaken for smoke. Thus any wavelength selective build up ofcontaminants on the optical surfaces can be problematic.

It is a problem in the field of video surveillance, and similar fieldswhich have remotely located optical devices (such as cameras), thatinsects or other foreign bodies may from time to time land on theexposed surfaces of the optical components of the system and partly ortotally obscure the field of view of the optical components. Similarproblems may also arise in particle detection systems like beamdetectors which are exposed to bugs and other foreign bodies.Accordingly, there is a need to protect components of particle detectionsystems such as a beam detector and thereby to avoid or minimise falsealarms caused by such circumstances.

As described above, some embodiments of the present invention mayinclude separate light emitters in the transmitter which are configuredto emit light in different wavelength bands. Most preferably the lightemitters are LEDs. Over time the output of the LEDs may vary in eitherabsolute or comparative intensity or both. With the dual wavelengthsystem variations in absolute intensity can be tolerated to a certainextent so long as the relative measure of intensity used by the systemfor detecting particles remains substantially constant. However,relative variations in the output intensities of the two light emittersmay create faults or false alarms. This is particularly the case whenthe output signal from the UV LED reduces compared to the output of theinfrared LED.

It is known to use beam detectors to monitor large areas by using beamsover say, 150 meters long or, in relatively confined spaces requiring abeam length of eg. only 3 meters. In conventional beam detector systemsan identical light source and receiver can be used for these two verydifferent applications, i.e. 150 meter separation or for 3 meterseparation. This is made possible by either adjusting the gain on thereceiver or turning down the transmitter power according to theseparation between the transmitter and the receiver.

However, the applicant's previous applications discussed above, and theexample of FIG. 3 show a beam detector which may include more than onetransmitter for each receiver. This presents its own particularproblems, in that it is possible to have multiple transmitters set atvastly different distances from the receiver. For example, consider aroom of the type illustrated in FIG. 57. This room 5700 is generallyL-shaped and has a receiver 5702 mounted at the external apex of theL-shape. Three transmitters 5704, 5706, 5708 are positioned around theroom 5700. The first transmitter 5704 is located along one arm of the L.A second transmitter 5706 is located in a position 90° from the firstreceiver 5704 at the end of the other arm of the L. A third transmitter5708 is mounted across the apex of the L-shape from the receiver 5702.As will be appreciated the distances between the transmitters 5704 5706and the receiver 5702 are much longer than the distance between thetransmitter 5708 and the receiver 5702. As a result, the level of lightreceived from each transmitter will be very different. Moreovertransmitter 5708 may be so close to the receiver that it saturates itslight receiving element.

Other disadvantages may also arise, for example, from time to time, aninstaller may take advantage of the reliable performance of beamdetectors and install a system outside the manufacturer'sspecifications. For example, although beam detectors are often intendedto operate with a substantial separation between the transmitter andreceiver an installer may extend this distance to provide a systembeyond that recommended by the manufacturer or allowed by regulations.In some cases an installer of the particle detector may not know of thelimits of operation of the receiver for the light source providedtherewith.

In such circumstances an installed particle detector may operatesatisfactorily at initial installation, but sometime followinginstallation, cease to operate correctly. This may occur, for instancewhere the particle detector or was initially installed close to, butbeyond its design limits. Over time, changes may occur to the equipmentor environment, which gradually alter the received signal strength dueto reasons other than the presence of particles in the beam. Thesechanges may be caused by, for example, component ageing, gross alignmentdrift, or contamination of optical surfaces. Such system drift wouldordinarily be handled by the system if it had been set-up within itsdesign limits. However, when the system is set up outside these limits,degradation of performance and the associated occurrence of faultconditions may occur prematurely or repeatedly.

Furthermore, it is desirable to be able to calibrate and/or test such abeam detector by simulating the presence of smoke using a solid object.Such a test is a requirement of standards bodies testing for beamdetectors. For example, the European EN 54-12 standard for ‘Biodetectionand fire alarm systems. Smoke detectors. Line detectors using an opticallight beam’.

In prior art testing methods the testing of beam detectors employs alight filter that partially obscures the projected light beam tosimulate the effect of smoke. The filters used usually consist of a meshof fibres, or dye-loaded plates or transparencies with printed featureswhich obstruct all visible and near visible wavelengths by substantiallythe same amount in a repeatable fashion. The present inventors haverealised that this type of filter may not be suitable for use with abeam detector of the type described above.

In a preferred embodiment of the system described in FIGS. 1 to 3, thelight sources are configured to include a plurality of light emitters,wherein each light emitter is adapted to generate light in a particularwavelength band. Moreover, the separate light sources are arranged toemit light at different times in order that a monochromatic imagingelement may be used. The direct result of the use of separate lightemitters is that there is some separation between the two light emittersin the light source, and thus the light will travel over slightlydifferent, although closely adjacent, beam paths through the interveningspace between the light source and receiver. This provides a risk that asmall object such as an insect on the transmitter could affect one lightpath more than the other and so affect the reading of the receiver. Thismay induce a false alarm or unnecessary fault condition.

Conventional beam detectors require careful alignment at the time ofinstallation. Such alignment aims to ensure that in normal conditions,free from particles, light enters the sensor so as to capture themajority of the transmitted beam, and to in turn maximise sensitivity toan obscuration. This calibration may be slow and therefore costly toperform. Moreover, it may need to be repeated as the physicalenvironment changes, for example because of small movements in thestructure to which a beam detector is attached. As stated above, theinventors have previously proposed a particle detector in PCT/AU2008/001697, filed 10 Jun. 2009 in the name of Xtralis Technologies Ltd(the specification of which is incorporated herein, by reference, in itsentirety) which includes a receiver which has a light sensor comprisingmatrix of light sensor elements, e.g. CCD (charge-coupled device) imagesensor chip, or CMOS (complementary metal-oxide-semiconductor) imagesensors such as in a video camera, or other receiver that is capable ofreceiving and reporting light intensity at a plurality of points acrossits field of view. Each sensor element in the receiver produces a signalthat is related to the intensity of the light that it receives. Thesignals are transmitted to the controller, where a particle detectionalgorithm is applied to the received image data. Compared to asingle-sensor receiver, the receiver in this particle detector has awider field of view but lower noise and has the ability to independentlymeasure light at a wider range of points within this field of view.

Because each sensor element has an inherent noise level, the overallsignal-to-noise ratio of the system can be improved by focusing thetarget (i.e. beam image) on a single sensor element. However, this maynot yield optimal results.

The above mentioned type of sensor e.g. CCD's and the like, aresometimes subject to a phenomenon created by the image processingalgorithm used for the receiver, known as staircasing, wherein adjacentpixels or adjacent groups of pixels have significantly different values.The physical structure of the sensor also has non-responsive “gaps”between sensor elements that produce no signal. Because of theseeffects, any variation in the alignment of the smoke detector componentscan potentially create a large variation in the measured light intensitylevel.

For example, because of the small size of the focused target, a verysmall movement of the receiver or the transmitter could cause the targetto move onto an entirely different sensor element with a very differentinherent noise level or response compared to the previous pixel on whichit was focused. It may also fall into a position, where all, or anon-trivial part, of the received beam falls into one of theaforementioned “gaps”. The resulting variation in the image intensity asdetermined by the controller can thus potentially cause the controllerto falsely detect smoke.

To partly ameliorate this problem, the detector can be adapted to trackthe target across the light sensors over time to enable a smokedetection to be performed on the signals from the correct sensors overtime. However, to properly determine the image intensity, the controllerwill be required to ascertain the inherent properties of different lightsensors used over time. Doing so requires system resources such asprocessing cycles and power. Also it is not always possible for thecontroller to make this determination.

In beam detectors an additional problem that may arise is interferencefrom ambient light within the volume being monitored. The ambient lightcan either be from sunlight illuminating the volume or artificiallighting used to illuminate the space. Accordingly, beam detectorsrequire mechanisms for minimising the impact of this light. This problemis compounded by the conflicting requirement that the light sources ofthe beam detector should be relatively low powered so that they minimisepower consumption, are eye safe and do not create a visible nuisance. Inprior art beam detectors which use a single wavelength of light a filteris typically used to reduce the signal from ambient light. In the caseof an infrared beam detector this is generally a low pass filter thatremoves substantially all visible and UV light. However, this isinappropriate for a multiple wavelength system as described herein.

In the preferred embodiment of the system described above the particledetector is powered at the receiver directly from the fire alarm loop.This minimises the installation costs of the device in that it obviatesthe need for dedicated wiring for supplying power or communicating withthe detector. However, the fire alarm loop usually only provides a verysmall amount of DC electrical power for the detector. For example, anaverage power consumption of about 50 mW may be desirable for such adetector. However with current technology the power consumed duringvideo capture and processing may be far above the 50 mW that isavailable from the loop. To address this problem a separate power supplycould be used, but this is costly since standards for fire safetyequipment are onerous, e.g. they require a fully approved and supervisedbattery backed supply, and fixed mains wiring.

The limited supply of power also limits the optical power output of thetransmitter. The limited optical power output in turn limits the signalto noise ratio of the measured signal. If the signal to noise ratio ofthe system degrades too far, the system may experience frequent orcontinual false alarms.

In some systems, the signal to noise ratio can be enhanced by employinglong integration or averaging times at the receiver. However systemresponse times, which are usually between 10 and 60 seconds, must beincreased to higher levels if long integration times are used. This isundesirable.

In addition to using a beam detector for smoke detection it is oftendesirable to use other sensor mechanisms for detecting additional oralternative environmental conditions or hazards, for example CO₂ gasdetection or temperature detection. The detectors conventionally use awired or radio communication link to signal an alarm or fault conditionto fire alarm control panel or like monitoring system. As such theselinks often add significant cost and potential reliability issues to thealarm system.

In some systems the present inventors have determined that it can bebeneficial to operate at least some components, and most advantageouslythe transmitter on a battery. An exemplary component is described in theapplicant's co-pending patent application no. PCT/AU 2009/000727, filedon 26 Jun. 2008, the contents of which are incorporate herein byreference for all purposes.

However, a problem that can arise in a battery powered component of aparticle detector is that over time, the batteries of the component willbecome discharged and the component will ultimately fail. Such failurewill potentially require an unscheduled maintenance call out for thedevice to be repaired and recommissioned. In a smoke detectionapplication this is particularly problematic as the equipment is used ina life-safety role and faults are required to be rapidly remedied. Theproblem can be remedied by performing preventative maintenance butultimately this may amount to performing unnecessary servicing andreplacement of units that have a significant amount of battery liferemaining and therefore is costly and wasteful of materials.

Unfortunately, variations in individual battery performance andenvironmental conditions make simply scheduling routine replacementperiods unreliable and potentially wasteful. One apparent solution tothe problem is to equip the component with an indicator of batterystate, however this has a disadvantage of adding cost, and the indicatoritself is power consuming which further reduces battery life. Moreover,it requires regular direct inspection of the indicator on the componentwhich, in the case of a beam detector, may be particularly inconvenient.

In beam detectors such as that described in relation to FIG. 3 i.e.where a plurality of beam detectors are formed by correspondingtransmitter and receiver pairs, such that two or more beams eitherintersect or pass through a common region of air, sufficiently close toeach other that their points of intersection can be mapped to addresseswithin the region being monitored, a problem may arise in that any oneof the subsystems may be affected by environmental conditions or systemproblems that do not affect the other subsystem. Such issues generallyforce a reduction in achievable sensitivity or increase the rate ofunwanted false alarms.

Reference to any prior art in the specification is not, and should notbe taken as, an acknowledgment or any form of suggestion that this priorart forms part of the common general knowledge in Australia or any otherjurisdiction or that this prior art could reasonably be expected to beascertained, understood and regarded as relevant by a person skilled inthe art.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a beam detectorarrangement comprising a transmitter adapted to transmit one or morebeams of light having a predetermined characteristic over a field ofillumination and a receiver having a field of view of the receiver andadapted to receive a beam of light transmitted by the transmitter;

the beam detector being installed to protect a monitored volume whichincludes a structure having one or more reflective surfaces within thefield of illumination of the transmitter and the field of view of thereceiver;

the beam detector including a processor adapted to determine whether alight beam received at the receiver possesses one or more predeterminedlight characteristics.

In the event that the one or more characteristics are possessed theprocessor can be adapted to determine that a beam of light from thetransmitter is received. In the event that a received beam does notpossess the one or more characteristics the processor can determine thata beam of light from the transmitter is not received. Alternatively theprocessor can determine that the beam of light received is a reflectionof the transmitted beam.

The beam detector arrangement can include signalling means adapted tosignal a fault condition in the event that the processor determines thata beam of light from the transmitter is not received and/or a reflectedbeam is received.

In a second aspect the present invention provides a method fordetermining whether a beam of light received by a receiver of a beamdetector is a directly transmitted beam or a reflected beam. The methodincluding receiving the beam at a receiver and measuring one or morepredetermined characteristics of the beam, and depending on the extentto which the predetermined characteristic is present in the beamdetermining if the received beam is a directly transmitted beam or areflected beam. In the event that the one or more characteristics of thereceived beam do not substantially match one or more predeterminedcharacteristics of the transmitted beam the method can include,determining that the received beam is a reflection. The beamcharacteristics can include relative strength of two or more wavelengthcomponents in the received beam and/or received polarisationcharacteristics of the beam.

In a further aspect the present invention provides a receiver for a beamdetector, the receiver including the plurality of image sensors, eachimage sensor including a plurality of sensor elements, said imagesensors being arranged to have at least partially overlapping fields ofview. The receiver can additionally include an optical arrangementadapted to form an image on each of the two sensors. The receiver canadditionally include image analysis means to analyse an image from morethan one of the plurality of image sensors to determine an angularposition of an image component within the field of view of a pluralityof the sensors. The image component can be one or more beams transmittedby a light source of a beam detector.

In a further aspect the present invention provides a receiver for a beamdetector, the receiver including:

-   -   one or more sensors including a plurality of sensor elements to        receive a beam of light from a transmitter;    -   processing means in data communication with the one or more        sensors to receive and process image data therefrom; and    -   input means adapted to receive an input representative of a        number of beams which are to be received from one or more        transmitters of the beam detector.

Preferably, the input means can include one or more switches (e.g. DIPswitches), or by providing a data input interface such as a serial port,or the like, over which data may be provided to the processor means, ormemory associated therewith.

In a further aspect, the present invention provides a beam detectorincluding: one or more light sources adapted to transmit said beam oflight across a region being monitored; one or more receivers arrangedwith respect to the transmitter and the volume being monitored such thatlight from the transmitter arrives at the receiver after traversing atleast a part of the volume being monitored.

In certain embodiments of the present invention the beam detector systemmay include one or more light blocking baffles arranged with respect tothe volume being monitored and the transmitter and/or receiver such thatno reflections from a surface within a field of illumination a lightsource and a field of view of a light receiver of the beam detectorarrive at the receiver.

In preferred embodiments of the beam detector the light receiver is madein accordance with one of the aspects of the invention described herein.

In certain embodiments of the present invention, the transmitter of thebeam detector is made in accordance with an embodiment of any one of theaspects of the present invention.

In one aspect the present invention provides a transmitter for a beamdetector transmitter including one or more light sources adapted togenerate light in a spatially distinct beam pattern. Preferably, thespatially distinguishable beam pattern is not symmetrical in at leastone plane. The spatially distinguishable beam pattern can include apattern of individual light beams having distinguishablecharacteristics. The characteristics may be wavelength characteristics,polarisation characteristics or modulation characteristics which aredistinguishable from each other. Other characteristics may also be used.For example, in a preferred form, this distinguishable pattern caninclude a pair of distinguishable light beams. A single light source canbe used in some embodiments of the transmitter. In this case, the imageof the beam which is formed by a receiver must be such that a shape ofthe light source is directionally distinguishable. For example, theimage of the light source can be ‘L’ shaped such that up and down andleft and right can be distinguished from an image of the light source.

In a beam detector including a transmitter of the above type, thepresent invention, in a further aspect, also provides a method ofdetermining whether a beam received at a receiver is transmitted by adirect or reflected path, the method including:

-   -   arranging a light source and receiver such that the beam        transmitted by the source is received at the receiver; and    -   orienting the light source with respect to an adjacent surface        within the field of illumination of the light source and field        of view of the receiver, such that a direct image of the light        source and reflected mirror image of the light source from the        surface are distinguishable at the receiver.

This step of aligning can include aligning the light source such thatits image is not symmetrical in the direct and reflected images.

In a further aspect the present invention provides a method ofdistinguishing a directly received beam from a reflected beam in a beamdetector system, the method including receiving an image containing twoimage segments which potentially correspond to beams transmitted by theparticle detector;

-   -   determining a brightness of each of the received beams; and    -   determining that a brightest one of the received beams is the        directly received beam.

In a further aspect of the present invention there is provided a methodof determining which one of a plurality of received beams is directlyreceived from a light source and which is received by a reflection froma surface, the method including:

-   -   determining which of the received beams is received at a sensor        element of a light sensor of a receiver of the beam detector        that is furthest perpendicularly from the reflecting surface;        and    -   designating the determined beam image as the direct beam image.

In a first aspect there is provided a beam detector including:

-   -   a light source adapted to transmit a beam of light with a first        polarisation state;    -   a light receiver adapted to receive light in a second        polarisation state and output a received light level; and    -   a controller adapted to analyse the received light level and        apply alarm and/or fault logic and if a predetermined fault        condition exists, to initiate an action.

In one embodiment the first and second polarisation states are parallel.

In another embodiment the first and second polarisation states areoffset from each other. They may be orthogonal.

The beam detector can include a light source adapted to transmit asecond beam of light with a third polarisation state. The first andthird polarisation states are preferably different. Most preferably theyare orthogonal. The first and second light sources can be a common lightsource. The third and second polarisation states can be the same.

The beam detector can also include a light receiver adapted to receivelight in a fourth polarisation state.

The second and fourth polarisation states are preferably different. Mostpreferably they are orthogonal. The fourth and first polarisation statescan be the same.

One or both of the light receiver or transmitter can include apolarising filter, or a plurality of interchangeable filters.

A component of a beam detector system including:

-   -   at least one electro-optical component configured to emit light        or receive light in a first spatial distribution; and    -   an optical subsystem arranged with respect to the        electro-optical component such that the first spatial        distribution is adjusted to form a second spatial distribution,        wherein        -   the relative extent of the first spatial distribution along            two non-parallel axes are different to the relative extent            of the second spatial distribution along the same axes.

Preferably the axes are orthogonal to each other. Most preferably one isinterdict to be a vertical axis and the other a horizontal axis.

Preferably the second spatial distribution is relatively widerhorizontally than vertically when compared to the first spatialdistribution.

The optical subsystem can include an anamorphic lens, or other‘wide-screen’ optical system.

The electro-optical component can be an image sensor. Theelectro-optical component can be a light emitter e.g. an LED, laserdiode.

A further aspect of the present invention provides a light source for abeam detector including:

-   -   at least a light emitter to generate a beam of light; and    -   an optical subsystem for controlling the angular dispersion of        the beam of light wherein the optical subsystem is adapted to        shape the beam of light such that it has a larger angular        dispersion along one axis than another.

Preferably the shape of the beam is wider than it is high. The beam canbe shaped such that it has a horizontal angular dispersion of between 5and 25 degrees. Most preferably it is between about 10 and 15 degrees.

The vertical dispersion can be between 0 and 10 degrees. Most preferablyit is between about 3 and 5 degrees.

In a yet another aspect the present invention provides a receiver for abeam detector including:

-   -   a light sensor capable of providing an output representative of        a sensed light level at a plurality of positions on the sensor;        and    -   an optical subsystem adapted to receive light in a field of view        having a first shape and direct it onto the light sensor in an        image of a second different shape.

Preferably the optical subsystem includes an anamorphic lens. The fieldof view of the optical subsystem is preferably wider in one directionthan another. Preferably it is wider than it is high.

The field of view of the optical subsystem can be defined by a maximumlight acceptance angle in one direction and a maximum light acceptanceangle in another direction.

Preferably the maximum horizontal acceptance angle is 90 degrees orless. However it could be more in some cases.

Preferably the maximum vertical acceptance angle is 10 degrees or less.

A further aspect of the invention, in broad outline relates to the setup of particle detection apparatus wherein a visual alignment deviceincorporated with or attached to the particle detection apparatus isdirected towards a target and is used to accurately align the apparatusat the time of installation, or when adjustment of alignment isnecessary. The visual alignment device and the optical elements in theparticle detector will have a fixed alignment relative to each other.The visual alignment device may comprise a visual beam generator whichprojects a visually observable light beam towards the remote surface, orit may comprise a video camera which receives an image of the remotesurface and displays the image of the surface on a display screen.

One aspect of the invention provides a component of a smoke detectorcomprising:

-   -   an optical module including one or more light sources and/or one        or more light receivers; mounting means for mounting the optical        module to a support surface;    -   an articulated connection located between the mounting means and        the optical module; and    -   a visual alignment device fixed to move with the optical module        for assisting in aligning the light source or sources and/or        receiver or receivers, relative to a target.

Optionally the visual alignment device comprises one or more sockets inthe optical module in which an alignment beam generator can be inserted.

The articulated connection may include one or more locking means forlocking the orientation of the optical module relative to the mountingmeans. The articulated connection may comprise a ball and cup joint,capable of allowing the optical module to be tilted relative to themounting means through a relatively large arc of tilt, the locking meansadapted to lock the ball to the cup in a selected orientation. Thelocking means may comprise a screw member which engages in a threadedbore in the cup and contacts the surface of the ball to lock the balland cup together. Optionally the screw is accessible via the visualalignment device.

In an alternative configuration of the invention provides a component ofa smoke detector comprising:

-   -   an optical module including one or more light sources and/or one        or more light receivers;    -   fixed mounting means for mounting the optical module to a        support surface;    -   an articulated mounting means located between the optical module        and one or more light sources or light receivers; and    -   a visual alignment device fixed to move with the light source or        sources and/or receiver or receivers, to assist in aligning the        light source, sources and/or receivers relative to a target.

Optionally the visual alignment device comprises one or more sockets inthe articulated mounting means in which an alignment beam generator canbe inserted.

The articulated connection may include one or more locking means forlocking the orientation of the optical module relative to thearticulated mounting means. The articulated connection may comprise aball and cup joint, capable of allowing the optical module to be tiltedrelative to the mounting means through a relatively large arc of tilt,the locking means adapted to lock the ball to the cup in a selectedorientation. The locking means may comprise a screw member which engagesin a threaded bore in the cup and contacts the surface of the ball tolock the ball and cup together. Optionally the screw is accessible viathe visual alignment device. Alternatively a rotatable mount can beused.

The visual alignment device may comprise a laser housed in or mounted ona cylindrical tube or shaft sized to be a sliding fit in the beamalignment means. Optionally the laser forms part of a tool for lockingthe articulated connection. The laser may flash to assist in visualidentification.

Alternatively the visual alignment device may comprise a video cameramounted to move with the housing, and able to generate an image of thetarget, the image including sighting means which, when aligned with thetarget will indicate that the optical component is operationallyaligned. The housing may include a video camera mount which, when thecamera is mounted thereto aligns the camera with the housing such thatthe camera has a field of view aligned in a direction in a knownorientation relative to the light source. Optionally the knownorientation is axially aligned with light emitting from the lightsource.

The component can be, for example a transmitter, receiver or target fora particle detector, such as a beam detector.

Another aspect of the invention provides a method of aligning acomponent of a smoke detector comprising:

-   -   mounting the component in an initial orientation to a support        surface, the component including a visual alignment device;    -   determining the orientation of the component by visually        observing an output of the visual alignment device;    -   adjusting the orientation of the component by monitoring the        visual alignment device until the component is in a selected        operating orientation; and    -   fixing the component in said operating orientation.

The method can include removing the visual alignment device from thecomponent.

The orientation of the component could be determined by observing eitherof a position of an alignment light beam emitted from the visualalignment device at a location remote from the support surface, orobserving an image of the remote surface generated by a camera of thevisual alignment device.

A further aspect of the invention provides an alignment tool comprising:

-   -   a shaft having a handle;    -   a driver actuatable by the handle;    -   a visual alignment device in a fixed or known orientation        relative to the driver; and    -   a shaft and a handle.

Further there is provided for the visual alignment device to comprise alaser which is located in a casing, and for a handle to have a recesstherein shaped to receive the casing. The laser will typically be abattery powered laser with an on/off switch so that the laser may beswitched off when not in use. The shaft may be straight or may have anelbow therein, depending on the configuration of the apparatus withwhich the tool is to be used. Alternatively the visual alignment devicemay comprise a video camera.

An aspect of the invention provides a visual alignment tool having:

-   -   engagement means for engaging with and aligning the visual        alignment tool relative to a particle detector component; and    -   visual targeting means for providing a visual indication of the        alignment of the particle detector component when so engaged.

The visual targeting means may be a camera, but is preferably a meansfor projecting visible light. The visible light could be a simple beamas in a laser pointer, or more complex patterns such as cross hairs. Themeans for projecting may flash to assist in visual identification. Thevisual targeting means is preferably battery powered, and may include anon/off switch so that it may be switched off when not in use.

The engagement means is preferably an elongate projection receivablewithin a recess within the particle detector component. Preferably thevisual targeting means is coaxially aligned with the engagement means.

The visual alignment tool preferably includes an elongate handle and ashaft, the shaft projecting from an end of the handle and beingcoaxially aligned therewith, wherein at least a portion of the shaftforms the engagement means. The shaft and recess may be cylindrical andsized for a sliding fit therebetween.

The visual targeting means is preferably arranged at the other end ofthe handle. Optionally the visual targeting means may be removable fromthe handle.

The visual alignment tool may include a driver for engaging with andactuating a locking means of the particle detector component.

The driver is preferably formed at an end of the shaft distal from thehandle and rotatable about the axis of the shaft to actuate the lockingmeans. The driver may be, for example, an Allen key (hex), Phillips heador other propriety shape e.g. a triangle. Ideally the driver is shapedfor engagement with the locking means in only a single relativerotational orientation, e.g. the drive may be a non-equilateraltriangular projection receivable in a complementary recess, so that therotational orientation of the visual alignment tool is indicative of thestate of the locking means. Visible indicia may be provided on the toolto aid in said indication.

In this aspect the invention also provides a particle detectorcomponent;

-   -   the component including a mounting portion, an optical module,        and locking means;    -   the mounting portion being fixedly attachable to a mounting        surface;    -   the optical module being articulated relative to the mounting        portion for alignment relative to a target and including means        for enabling a visual indication of said alignment; and    -   the locking means being actuatable to lock the optical module        relative to the mounting portion in a selected alignment.

The term ‘target’ as used herein is intended to be interpreted broadly,and may include an actual target mounted at the remote location forreflecting the source light back to a receiver. The target may alsohowever simply refer to a remote surface if reflected light from thatremote surface is monitored by the receiver or even a desired point onwhich a component should be aligned, e.g. the receiver could be a targetfor a light source or vice versa.

The means for enabling a visual indication could be a visual targetingmeans, including an electro optical device such as a camera or laserpointer, but is preferably an engagement feature for cooperating with avisual alignment tool incorporating visual targeting means.

Preferably the optical module includes an elongate recess forming theengagement feature. The recess preferably has at least one open end andis arranged so that the axis of the recess projects toward the targetwhen the optical module is in alignment with it. The recess may projectin a direction parallel to a limit of a field of operation of theoptical module or in some other known physical relationship with thespatial optical characteristics of the optical module.

The locking means is preferably actuatable by the visual alignment tool.The locking means preferably includes a driven member located within therecess and engageable with a driver of the visual alignment tool toactuate the locking mechanism. Preferably it is adapted to berotationally driven about the axis of the recess to a selectedorientation to actuate with locking means. The driven member ispreferably shaped for engagement with the driver of the visual alignmenttool in only a single relative rotational orientation, e.g. the drivermay a non-equilateral triangular projection receivable in acomplementary recess formed in the driven member, so that the rotationalorientation of the visual alignment tool is indicative of the state ofthe locking means. Indicia may be provided on the component to aid insaid indication.

Preferably one of the optical module and the mounting portion, mostpreferably the optical module, is captured within the other portion,said articulation being effected by a spherical sliding fit between theoptical module and the mounting portion. The driven member may be a grubscrew within one of the optical module and mounting portion, androtatable to engage the other of the optical module or mounting portion.But preferably, the optical module includes a brake shoe and a cam,wherein the cam is arranged to be driven by the driven member and inturn drive the brake shoe to, frictionally or otherwise, engage themounting portion and thereby lock the optical module relative to themounting portion. The cam may be attached to the driven member orintegrally formed therewith. The braking shoe may be biased towards aretracted, non-braking, position.

The optical module may include a simple optical element, such as a lensor a mirror. For example, a mirror alignable for redirecting a beam toor from a fixedly mounting electro-optical element. In this case themirror and electro-optical element may be mounted in a housing.

Preferably the optical module includes an electro-optical element suchas a light emitting element or elements or light receiver. Theelectro-optical element could be camera.

Preferably the particle detector component is configured to operativelyconnect a circuit, to enable operation of the electro-optical element,to a power supply when said locking means is actuated. For this purpose,a switch may be associated with the driven member. For example, thedriven member may carry at a point at a radius from its axis a magnetwhich is arranged to act on a reed switch when the driven member isrotated to the selected orientation.

This aspect of the invention also provides a combination of the particledetector component and the visual alignment tool, and methods ofinstalling, and aligning, a particle detector component.

There is provided a method of aligning a particle detector component,the particle detector component includes an optical module, a mountingportion and locking means, the method includes:

-   -   articulating the optical module relative to the mounting portion        to align a visual indication of orientation with a target.

Preferably the method includes actuating the locking means to lock theoptical module in said alignment.

Preferably the method further includes engaging with the optical moduleof the particle detector component a visual alignment tool to providesaid visual indication of the orientation of the optical module; and,

-   -   disengaging said visual alignment tool.

Said actuation preferably includes rotating said visual indication tool,and most preferably simultaneously connects an electro-optical componentto a power supply.

The method of installing the particle detector component includes:

-   -   fixedly mounting a mounting portion of the particle detector        component to a mounting surface; and    -   aligning the particle detector component in accordance with the        aforedescribed method.

In a preferred form the step locking the optical module and connectingthe electro-optical component to a power supply.

In another aspect the invention provides a smoke detector component:

-   -   the component including a mounting portion, an optical module,        locking means and activation means;    -   the mounting portion being fixedly attachable to a mounting        surface;    -   the optical module including a electro-optical element and being        articulated relative to the mounting portion for alignment        relative to a target;    -   the locking means being actuatable in response to an installer        input to lock the optical module relative to the mounting        portion in a selected alignment; and    -   the activation means configured to operatively connect the        electro-optical element to a power supply in response to said        installer input.

In a further aspect the present invention provides, a component of aparticle detector including an electro-optical component adapted to atleast transmit or receive an optical signal over an angular region, anoptical assembly adapted to redirect an optical signal said opticalassembly an electro-optical component being mounted relative to eachother such that the electro-optical component receives or transmitsoptical signals via the optical assembly, wherein: the orientation ofthe optical assembly is adjustable with respect to the electro-opticalcomponent to enable the direction of optical signals transmitted orreceived by the component to be changed.

Preferably the component includes a housing in which the electro-opticalcomponent and optical assembly are mounted; and an aperture throughwhich an optical signal may pass.

The mounting means can be adapted to mount the optical assembly rotablywith respect to the housing. The mounting means is preferably a frictionfit with a recess in the housing. The mounting means preferably includesan engagement means engagable by a actuating tool to allow rotation ofthe optical assembly. The engagement means can be adapted to engage withan actuating tool as described herein.

The optical assembly can include a mirror to reflect an optical signal.

The electro-optical component can be a light sensor including aplurality of sensor elements. The light sensor is preferably a cameraadapted to capture a series of images.

According to an aspect of the invention there is provided a particledetector assembly comprising a first module having an actuator and asecond module configured to be mounted to the first module. The secondmodule comprises electro-optical system for use in a beam-detectionsystem and a power source operable to provide electrical power to theelectro-optical system. The second unit also includes a switchresponsive to the actuator. When the second module is mounted to thefirst module, the actuator causes the switch to operatively connect thepower source to the electro-optical system.

In one arrangement the actuator is a magnet, and a reed switch is usedto detect the proximity of the magnet when the two modules areassembled.

In broad concept, one aspect of this invention, may improve systemperformance in cases where contamination of the optical surface affectsboth wavelengths by substantially the same amount. In this aspect, verygradual reduction of the received signals are compensated by an increaseof the effective overall receiver gain of both signal channels, using atime constant that is chosen to be far longer than might cause a realfire to go undetected; for example a week.

Thus, in one aspect the present invention includes detecting a long timedrift in received light level in a particle detection system; andincreasing gain of a detection circuit to compensate for the drift. In asystem with multiple illuminations, e.g. at different wavelengths awavelength dependent gain increase can be made.

This concept can be extended such that where the contamination of theoptical surface affects the shorter wavelength by more than it does thelonger wavelength, as may occur when the contamination consists largelyof very small particles such as are present as a result of smokepollution, the very gradual reduction of the received signals areindividually compensated by an increase of the effective overallreceiver gain of each signal channel separately, again using a timeconstant that is chosen to be far longer than might cause a real fire togo undetected; for example a week.

In a first aspect the present invention provides a light source for usein a particle detection system, the light source adapted to transmit: afirst light beam in a first wavelength band; a second light beam in asecond wavelength band; and a third light beam in a third wavelengthband, wherein the first and second wavelengths bands are substantiallyequal and are different to the third wavelength band.

The first and second wavelength bands may be in the ultraviolet portionof the EM spectrum. The third wavelength may be in the infrared portionof the EM spectrum.

The location from which the first light beam is transmitted from thelight source may be separated from the location from which the secondlight beam is transmitted from the light source. The separation may beapproximately 50 mm.

The light source may further include a first light emitter for emittingthe first and second light beams and a second light emitter for emittingthe third light beam. In this case the light source may further includea beam splitter for splitting light emitted from the first light emitterinto the first and second light beams. Alternatively, the light sourcemay include a first light emitter for emitting the first light beam, anda second light emitter for emitting the second light beam, and a thirdlight emitter for emitting the third light beam. The first, secondand/or third light emitters may be light emitting diodes.

The light source may further include a controller, the controllerconfigured to generate the first, second and third light beams in arepeated sequence. Preferably the repeated sequence includes thealternate operation of the first, second and/or third light emitters.

In a further aspect the present invention provides a light source foruse in a particle detection system, the light source including: a firstlight emitter for emitting a first beam of light; a second light emitterfor emitting a second beam of light; and an optical system including atransmission zone from which light from the first and second lightemitters is transmitted from the light source, wherein the opticalsystem is arranged such that obstruction of the transmission zone by aforeign body results in a substantially equivalent obstruction of boththe first and second beams of light.

The first and second light emitters can be semiconductor dies.Preferably they are semiconductor dies housed within a single opticalpackage.

The optical system can further include light directing optics fordirecting the first and second beams of light from the first and secondlight emitters to the transmission zone.

The light directing optics may be selected from a group including, butnot limited to, a convex lens, a Fresnel lens, and a mirror. Otheroptical components or combinations thereof can be used.

The transmission zone is preferably forms at least a part of anexternally accessible optical surface of the optical system. For examplethe outside surface of a lens, mirror, window, LED package or the like.

The optical system may further include beam shaping optics adapted tomodify a beam shape of either or both of the first and second beams oflight.

The beam shaping optics may provide light transmitted from the lightsource with a beam divergence of approximately 10 degrees.

In this case the beam shaping optics may modify the beam shape of eitheror both of the beams to extend further in one direction than another,e.g. further horizontally than vertically.

The beam shaping optics can also modify the first and second beams sothat they have a different beam shape to each other. The beam shapingoptics may modify the first beam of light to have a wider beam shapethan the second beam of light.

The beam shaping optics may include one or more beam intensity adjustingelements configured to adjust the spatial intensity of the beam. Beamintensity adjusting elements may be selected from a group including, butnot limited to, an optical surface coating, a ground glass diffuser, andan etched glass diffuser.

The first light emitter may emit an ultraviolet light beam and thesecond light emitter may emit an infrared light beam.

The light directing optics and beam shaping optics can be combined intoa single optical element, or comprise an optical arrangement withmultiple optical elements. The optical elements can be transmissive orreflective elements.

In a further aspect the present invention provides a particle detectionsystem including a light source and a receiver, the light source asdescribed in any one or more of the above statements.

A light source for a particle detector, including: one or more lightemitters adapted to generate at least one light beam having a firstapparent size from a distant point of view; an optical system arrangedto receive the at least one light beam and transmit the at least onelight beam and adapted to cause the transmitted light beam to have asecond apparent size larger than the first apparent size from thedistant point of view.

The optical system preferably includes a beam diffuser. The diffuser canbe a dedicated optical component (e.g. a piece of etched glass) orformed as a surface treatment on an optical component that is used foranother purpose.

In another aspect, there is provided, a light source for a particledetector, including: one or more light emitters adapted to generate atleast one light beam having components in at least two wavelength bands,and optionally an optical system through which the one or more beamspass; the light emitter(s) and or optical system being configured tocause light in one of the at least two wavelength bands to have aspatial intensity profile which is different to light in another of thewavelength bands.

Preferably the beam width of light in one wavelength band is wider thanthe beam width of light in another wavelength band. Preferably light ina longer wavelength wavelength band has a narrower beam width than lightshorter wavelength wavelength band. Preferably the longer wavelengthband includes the infrared or red portion of the EM spectrum. Theshorter wavelength band can include light in the blue, violet orultraviolet portion of the EM spectrum.

In yet another aspect, the present invention provides a light emitterusable in a particle beam detector, the light emitter including: housingincluding a window portion through which light is emitted; means togenerate light in a plurality of wavelength bands; and a light sensitiveelement arranged within the housing and configured to receive a portionof the light in at least one or more of the wavelength bands emitted bythe means to generate light; one or more electrical contacts forenabling electrical connection between the means to generate light, thelight sensitive element and an electrical circuit.

Preferably the light emitter includes a plurality of light emittingelements adapted to emit light in a corresponding wavelength band.

The light sensitive element can be a photo diode or other lightsensitive circuit element.

Most preferably the light emitter elements are LED dies. Preferably thewindow portion of the housing can be adapted to control the shape of abeam of light emitted.

The housing can be an LED package.

In one form the light emitter includes a plurality of light emitters foremitting light in one or more of the wavelength bands. The plurality oflight emitters can be arranged within the housing to achieve apredetermined beam characteristic. In one example, the light emitterscorresponding to one wavelength band can be arranged to surround one ormore light emitters corresponding to another wavelength band.

In a preferred form the housing can include means to minimise ambientlight arriving at the light sensitive element. For example, the meanscan include one or more filters which attenuate light outside thewavelength bands emitted by the light emitting elements. Alternatively,it can include one or more baffles or walls arranged within the housingsuch that the light sensitive element is substantially shielded fromreceiving direct light from outside the housing.

In a further aspect the present invention provides a method ofdetermining the output strength of a light emitting element of a lightsource in a particle detector. The method including illuminating thelight emitting element in accordance with a modulation pattern including“on periods” in which the light emitter is emitting light and “offperiods” in which no light is emitted by the light emitter; detectingthe output from the light emitting element in one or more on periods andone or more off periods; correcting the detected light output in one ormore on periods on the basis of the measured light level in the one ormore off periods. For example, the correction may including subtractingthe off period measurement from an adjacent on period measurement.Alternatively, the on or off periods may be accumulated or averaged oversome predetermined number of corresponding on or off periods todetermine the light output level.

In another aspect the present invention provides a light source for aparticle detector including at least one light emitter of a typedescribed herein.

The light source can include a modulation circuit component adapted tocontrol an illumination pattern of the light source and a feedbackcircuit component electrically connected to the light sensitive elementand adapted to receive an input therefrom and output a control signal tothe modulation circuit.

The modulation circuit can be adapted to vary one or more of:

-   -   the duration of illumination;    -   the intensity of illumination;    -   the voltage applied to a light emitter; or    -   the current applied to a light emitter,    -   on the basis of a level of or variation in the received feedback        signal received.

In a further aspect, the present invention provides a method in a lightsource of a particle detector, the method including: illuminating atleast light emitter of the light source according to a first modulationpattern, the pattern including a plurality of illumination pulses;receiving a feedback signal; adjusting the modulation pattern inresponse to the feedback signal.

The method can include adjusting at least one of:

-   -   the duration of illumination;    -   the intensity of illumination;    -   the voltage applied to a light emitter;    -   the current applied to a light emitter.

Preferably the feedback signal is generated by a light sensitive elementarranged to monitor the light output at least one light emitting elementof the light source.

The feedback signal can be a signal adapted to compensate for apredetermined characteristic of at least one light emitter of the lightsource. The predetermined characteristic can be a temperature responseof a light emitter.

In an embodiment of the present invention the step of adjusting themodulation pattern in response to the feedback signal can includeadjusting the modulation pattern to encode data relating to the outputintensity of at least one light emitter of the light source. Forexample, one or more modulation pulses may be, inserted into, oradjusted in, the modulation pattern to transmit light emitter outputdata to a receiver of the output of light.

In another aspect of the present invention there is provided a componentfor a beam detector including:

-   -   a housing having at least one side defining at least one        internal volume, the at least one wall including an optically        transmissive wall portion through which light may pass into or        out of the housing;    -   an electro-optical system within the internal volume adapted to        transmit and/or receive light through an optically transmissive        wall portion of the housing;    -   a foreign body detection system adapted to detect a foreign body        on or near an outer surface of the optically transmissive wall        portion, and including a light source adapted to illuminate the        outer surface and any foreign body on or near the outer surface;    -   a light receiver to receive light scattered from the foreign        body in the event one is illuminated, and generate an output        signal;    -   a controller adapted to analyse the output signal and apply        fault logic to determine the presence of a foreign body in the        event that one or more criteria are met and take an action.

The light receiver can be any one of:

-   -   a photo diode; and    -   part of a light sensor array used to detect particles in use.

The light source can be mounted within the internal volume.Alternatively it can be mounted outside the housing.

In a first aspect the present invention provides a method, in a particledetection system comprising one or more light sources and a receiverarranged so that light from the one or more light sources traverses anarea to be monitored for particles and is received by the receiver, anda controller programmed to monitor for the occurrence of one or morepredefined alarm and/or fault conditions based on at least one receivedlight intensity threshold; the method including: providing at least oneinitial light received intensity threshold for use by the controllerduring a commissioning period; and providing at least one firstoperational received light intensity threshold for use during anoperational period following the commissioning period.

Preferably a received light intensity threshold provided during thecommissioning period includes a minimum received light intensitythreshold, below which a fault condition may be indicated.

The received light intensity threshold provided during the operationalperiod can include a minimum received light intensity threshold, belowwhich either a fault condition or alarm condition may be indicated.

The minimum received light intensity threshold in the commissioningperiod can be above a minimum received light intensity threshold duringat least a portion of the operational period.

The method can further include: providing at least one secondoperational light intensity threshold, after the passing of a delayperiod, at least one second operational light intensity threshold beingfor use during at least part of the operational period following thedelay period.

The second operational intensity threshold can be based on one or moremeasurements of received intensity during the delay period.

This second operational light intensity threshold is preferably higherthan at least one first operational light intensity threshold. Thesecond operational light intensity threshold can be lower than at leastone initial light intensity threshold.

The method further include: determining the passing of the delay period.The step of: determining the passing of the delay period can beperformed automatically by the controller; and/or upon the receipt of ancommand signalling the end of the delay period.

If the received light includes a plurality of wavelength components themethod includes: determining the occurrence of at least one predefinedalarm condition based on the received light intensity at two or morewavelengths. The method can include, determining the occurrence of oneor more predefined alarm conditions based on combination of the receivedlight intensity at two or more wavelengths.

The method can further include, initiating the operational period afterthe commissioning period. Initiating the operational period can beperformed, automatically, e.g. based in a timer; or upon the receipt ofan initiation command.

In a further aspect the present invention provides a controller forparticle detection system comprising one or more light sources and areceiver arranged so that light from the one or more light sourcestraverses an area to be monitored for particles and is received by thereceiver, the controller being programmed to monitor for the occurrenceof one or more predefined alarm and/or fault conditions based on atleast one received light intensity threshold; said controller beingadapted to perform a method as described herein.

The controller can initiate an action upon the occurrence of one or morepredefined alarm and/or fault conditions. For example the action can bethe generation of an alarm or error signal.

The present invention also provides a particle detection systemincluding such a controller. The particle detection system can furtherincludes, a receiver for receiving light; one or more light sourcesarranged to emit light at one or more wavelengths, so that light fromthe one or more light sources traverses an area to be monitored forparticles and is received by the receiver. Preferably each light sourceis a light emitting diode. The receiver can include an array of lightsensor elements, e.g. the receiver can be a video camera.

A further aspect of the present invention can also provide a method ofcommissioning and operating a particle detection system, comprising:arranging one or more light sources and a receiver so that light fromthe one or more light sources traverses an area to be monitored forsmoke before being received by the receiver; and performing the methodwhich is an embodiment of the first aspect of the present invention.

In a further aspect there is provided a particle detection system formonitoring a volume, the system including: at least one transmitteradapted to transmit one or more light beams; a receiver adapted toreceive said one or more light beams from at least one transmitter aftertraversing the volume being monitored; a controller adapted todetermining the presence of particles in the volume on the basis of theoutput of the receiver; and means for determining a light outputintensity of a transmitter for use in particle detection.

The means for determining a light output intensity of the transmitterare associated with the transmitter. The means for determining a lightoutput intensity of the transmitter can include one or more filtersselectively able to be selectively positioned in a path of a beam oflight emitted by the transmitter. The transmitter can include mountingmeans configured to receive one or more filter elements to enable theintensity of the light output by the transmitter to be set to adetermined level.

The means for determining a light output intensity of the transmittercan include electronic control means adapted to electronically controlthe light output of the transmitter. The electronic control means caninclude one or more switches able to be manually controlled to selectthe a light output intensity for the transmitter.

The electronic control means may be in data communication with areceiver and is adapted to receive control information from the receiverrelating to the received light level form the transmitter, and isadapted to control the light output of the transmitter in response tosaid control information.

The means for determining a light output intensity of a transmitter foruse in particle detection can be associated with the receiver.

The transmitter can be adapted to transmit a plurality of signals atdifferent intensity levels. In this case the means for determining alight output intensity of a transmitter for use in particle detectioncan include, means associated with the receiver to determine thereceived light intensity level for the at the plurality of signalstransmitted at different intensity levels and compare the received lightintensity level to one or more criterion to determine the a light outputintensity of the transmitter for use in particle detection.

The transmitter can be adapted to transmit a repeated pattern of signalsincluding a plurality of signals at different intensity levels; and thereceiver can be adapted to selectively receive the one or more signalsin the repeated pattern determined to be used in particle detection.

The transmitter may include means for generating a repeated pattern ofsignals including a plurality of signals configured to produce differentreceived light levels at a receiver of the detection system.

The particle detection system is most preferably a beam detector.

The repeated pattern of signals can include signals transmitted withdifferent intensity levels. The repeated pattern of signals can includesignals of different durations.

In another aspect the present invention provides a transmitter for aparticle detection system, including: at least one light source togenerate a beam of light at least one wavelength; a housing in which thelight source is mounted; one or more filters selectively mountable withrespect to the light source for selectively attenuating the beam oflight.

The transmitter can includes a power source to powering the at least onelight source.

The transmitter can includes control circuitry to control anillumination pattern of the at least one light source.

In yet another aspect the present invention provides a receiver for aparticle detection system: at least one light sensor for measuring thelevel of light received from a transmitter of a particle detectionsystem; a controller to selectively activate the light sensor to receivesignals. The controller can be adapted to selectively activate the lightsensor to predetermined receive signals transmitted by a transmitter ofa particle detection system.

The predetermined signals transmitted by a transmitter can bepredetermined on the basis of the measured level of light received bythe sensor in an earlier time period.

The test filter comprising at least one sheet like filter element, andbeing configured to transmit light in a first wavelength bandtransmitted by the particle detector to a different extent than light ina second wavelength band transmitted by the particle detector.Preferably, the test filter transmits a light in a shorter wavelengthand emitted by the particle detector less than it transmits light in alonger wavelength band transmitted by the particle detector.

The test filter may include one or more sheets of filter material.

In one embodiment, a sheet or sheets of filter material may be formed ofa material such that differential transmission at the two wavelengths isachieved. Alternatively, one or more of the filter elements can betreated or impregnated with colour selective transmissive material. Thematerial in this case can be a dye.

In a preferred form the test filter includes a plurality of filterelements combined at such a manner to achieve predetermined transmissioncharacteristic. Preferably, the transmission characteristics mimic smokeat a predetermined concentration. The plurality of sheets can becombined in such a manner to provide a selectable transmissioncharacteristic.

In one embodiment, a sheet or sheets of substantially transparentmaterial to which has been added particles in a predetermined size rangecorresponding to particles to be detected by the detector under test.Most preferably, the particles are between 0.2 and 1.0 micron indiameter.

In a further embodiment a filter element may have a surface treatment tocreate a desired absorption characteristic. In one form, a filterelement can include a textured surface. The textured surface can becaused by, for example, mechanical abrasion, particle blasting, chemicalor laser etching.

In an alternative embodiment, third form, surface is printed withpredetermined number of dots corresponding to the predeterminedtransmission.

The filter elements may reflect or absorb light which is nottransmitted. However, absorption is typically more convenient.

In a first aspect present invention provides a receiver in a particledetector, said receiver including at least one receiver element adaptedto receive light and output a signal indicative of the received lightintensity at plurality of spatial positions; and an optical systemincluding at least one wavelength selective element configured toreceive light at a plurality of wavelengths simultaneously and transmitlight in two or more wavelength bands to the one or more sensor elementssuch that an output signal indicative of the received light intensity inthe at least two wavelength bands can be obtained.

In a preferred form the receiver is configured to measure the receivedlight intensity at a plurality of spatially separate positions in aplurality of wavelength bands substantially simultaneously.

In one form of the invention, the wavelength selective element caninclude a one or more filter elements placed in a light path before thereceiver. Most preferably, the filter element or elements includes amosaic dye filter. Alternatively, the wavelength selective element caninclude one or more light separating elements, e.g. prisms, diffractiongratings, or the like. In a further alternative, the light separationelement can be combined with the light sensor element, and comprise amulti-layered light sensitive element wherein respective layers of thelight sensitive element are configured to measure the intensity of lightin a corresponding wavelength band.

In a particularly preferred form, the wavelength bands of interestinclude an infrared band and an ultraviolet band. In this example, thewavelength selective elements can be adapted to be infrared selectiveand ultraviolet selective.

In some embodiments of the present invention the wavelength selectiveelement may be adapted to split the incoming beam of light intorespective wavelength components and direct each wavelength component toa corresponding sensor or subset of elements of a sensor.

In a further aspect the present invention provides receiver for a beamdetector including filtering means having multiple passbands. In oneform, the filtering means can include a multiple passband interferencefilter. For example, such a filter may be arranged to selectivelytransmit in first passband sensor a long wavelength and one or moreharmonics of that wavelength. For example, the filter can be designed totransmit substantially all of the light at 800 nanometers and 400nanometers while blocking a large majority of light at otherwavelengths. The filtering means can include a plurality of filters. Forexample, the plurality of filters can include more than one interferencefilter or plurality of dye filters or the like. Said plurality filterscan be arranged in a predetermined spatial pattern such that light indifferent passbands falls on different portions of a sensor of thereceiver.

In a further aspect of the present invention there is provided aprojected beam particle detector including a receiver of the typedescribed above. Preferably, the particle detector includes apolychromatic light source. Most preferably, the light source can beadapted to emit light in a plurality of wavelength bands simultaneously.In a particularly preferred embodiment, the light source includessynchronously operated monochromatic light sources. However, it mayalternatively include a polychromatic light source. The polychromaticlight source can include xenon flash tube or krypton light source.Alternatively, the light emitter may be a combination of aphosphorescent material and light emitter arranged to illuminate thephosphorescent material. The light emitter may, for example be an LED.

In a further aspect of the present invention there is provided atransmitter for a beam detector including a light source adapted to emitlight in a plurality of wavelength bands corresponding substantially torespective passbands of filter of the receiver of the beam detector.

In a further aspect the present invention provides a beam detectorcomprising at least one receiver and transmitter made in accordance withthe foregoing aspects of the invention.

According to one aspect of the invention, there is provided a smokedetector including:

-   -   a transmitter adapted to emit a light beam;    -   a receiver having a light sensor with a plurality of sensor        elements, for detecting the light beam, each of the sensor        elements being adapted to generate an electrical signal related        to the intensity of light impinging upon it;    -   the transmitter and received being arranged such that at least a        portion of a light beam from the transmitter is received by the        receiver;    -   a beam diffusing optics located in a path of travel of the light        beam to the receiver, for forming a diffused image of the light        beam on the light sensor, and    -   a controller that processes electrical signals generated by a        plurality of the sensor elements to determine the intensity of        the received beam, and apply alarm and/or fault logic to the        intensity data to determine if a predetermined condition is        fulfilled, and initiate an action if the predetermined condition        is fulfilled.

The beam diffusing optics can include a lens which focuses the lightbeam at a point which is not coincident with the sensor. The beamdiffusing optics can optionally include a diffuser which may be placedbetween the transmitter and the light sensors. A diffuser and lens canbe used together.

The diffused image of the beam preferably covers a plurality of sensorelements on the sensor of the receiver. For example it can cover between2 and 100 elements. Preferably it covers between 4 and 20 sensorelements, although it may be more depending on the size and density ofsensor elements on the sensor. The diffused image of the beam ispreferably larger than a sharply focused image of the beam would be.

The controller is preferably adapted to combine the received signalsfrom a plurality of sensor elements to determine the received lightlevel. In one form the measured light level from a plurality of sensorelements are added. Prior to adding the signal levels of eachcontributing sensor element can be weighted.

The controller may determine a centre-of-signal position correspondingto an image of a beam on the light sensors, and weight the signal fromeach sensor element according to a distance between each sensor and thecentre-of-signal position.

The transmitter may transmit a beam of light having components in two ormore wavelength bands.

According to another aspect of the invention, there is provided a methodfor detecting smoke, including:

-   -   transmitting a light beam from a transmitter toward a receiver        having a sensor comprising multiple sensor elements;    -   arranging a receiver so that it receives the beam;    -   forming a diffused image of the light beam on the sensor;    -   generating electrical signals related to the intensity of the        received light level detected by at least those sensor elements        of the multiple sensor elements on which the beam impinges;    -   determining the intensity of the received beam based on a        plurality of the signals;    -   applying an alarm and/or fault logic to the received determined        intensity; and    -   initiating an action if a predetermined alarm and/or fault        condition is determined.

The step of forming a diffused image of the beam optionally comprisesdefocusing the light beam such that it is focused at a position that isnot coincident with the light sensor.

Alternatively or additionally, the step of diffusing the beam mayinclude placing a diffuser between the transmitter and the sensor.

The step of determining the intensity of the received beam can includecombining a plurality of the received signals. The signals can beweighted in the combination. For example the method can includedetermining a centre of signal position of the diffused image of thebeam and weighting the signals according to the distance of theircorresponding sensor element from the centre of signal position.

In a first aspect the present invention provides a component for aparticle detection system including, a first processor adapted tointermittently receive data from an image capture device and to processsaid data; a second processor communicatively coupled with the firstprocessor and adapted to selectively activate the first processor.

The second processing device can be additionally configured to performone or more of the following additional functions of the particledetection system, communication with an external data communicationsystem connected to the particle detector; control of one or moreinterface components of the system; monitoring of a fault condition ofthe component, or the like.

Preferably the second processor is of lower power consumption than thefirst processor.

The component preferably also includes imaging means to receive one ormore optical signals from a transmitter associated with the particledetection system.

In a second aspect of the present invention there is provided a methodin a particle detection system. The method includes, monitoring anactivation period of a first processor using a second processor;activating the first processor in response to a signal from the secondprocessor; and performing one or more data processing steps with thefirst processor.

The method can include deactivating the first processor upon completionof one or more processing tasks.

The first processor is preferably adapted to process video data from areceiver of the particle detection system.

In one aspect the present invention provides a light source for aparticle detector, including:

-   -   at least one light emitter for emitting at least one beam of        light for illuminating a part of a region being monitored;    -   a battery for supplying electrical power to the light source;    -   a battery monitor for measuring at least one of the voltage of        the battery or its current output;    -   a controller configured to, control the illumination of at least        one light emitter of the light source and to receive at least        one of, the voltage of the battery or its current output, and to        determine a valve indicative of a remaining expected battery        life. Preferably, the controller is adapted, in the event that        the remaining expected battery life is less than a predetermined        period of time, to generate an indication of the remaining        expected battery life.

Preferably the light source includes an environmental monitor to monitoran environmental factor affecting the remaining expected battery life,e.g. temperature.

The predetermined period of time is preferably longer than a periodbetween scheduled, recommended or mandated servicing intervals for thelight source.

In another aspect the present invention provides environmentalmonitoring system including:

-   -   a beam detector subsystem including at least one transmitter        adapted to emit one or more beams of light across a region being        monitored and at least one receiver, adapted to receive at least        one beam of light emitted by a transmitter;    -   at least one additional environmental monitor adapted to sense        an environmental condition associated with the region being        monitored and to communicate an output, via an optical        communication channel, to a receiver of the beam detector        subsystem.

In a preferred form, the optical communications channel can beimplemented by modulating a beam output by one or more transmitters ofthe beam detection subsystem.

Alternatively, the optical communications channel can include a lightemitter associated with the one or more additional environmentalmonitors and arranged to lie within a field of view of a receiver of thebeam detector subsystem wherein the light emitter is adapted to bemodulated to communicate a sensed condition by an associatedenvironmental monitor.

In a particularly preferred form the light receiver of the beam detectorsubsystem can include one or more sensors including a plurality ofsensing elements adapted to measure a received light intensity at aplurality of spatial positions. Such a system can be used tosimultaneously monitor an optical communications channel and a particledetection beam of one or more transmitters of the beam detectorsubsystem.

In a further aspect of the present invention there is provided the beamdetection system comprising a plurality of beam detectors; at least onecontroller in data communication with the detectors and receiving anoutput from each of said beam detectors. The controller being adapted tocorrelate the output of at least a pair of beam detectors which arespatially substantially spatially coincident for at least part of theirbeam length and in the event that a predetermined correlation conditionexists determining that either particle detection event or a faultcondition has occurred. In one form, the correlation includes a temporalcorrelation. The correlation may include a particle detection levelcorrelation. In a simple form, the correlation may simply be performedby comparing whether the particle detection level of two or more beamdetectors are substantially equal, alternatively, a particle detectionprofile for a plurality of beam detectors may be compared to one anotherto determine the extent of correlation between them.

In another aspect of the present invention there is provided a method ofoperating a particle detection system including plurality of beamdetectors having beams that can substantially coincident at least onepoint. The method including receiving an output from the plurality ofbeam detectors, determining if a correlation condition exists between atleast two of the outputs, and if a predetermined correlation conditionexists; determining either a particle detection event or false alarmevent has occurred according to predetermined particle detection and/orfault logic. The alarm can include cross correlating a time varyingparticle detection profile of two detectors. It can also oralternatively include determining a correlation between a particledetection state i.e. an alarm level or alarm threshold crossing of thetwo or more detectors.

Throughout this specification the term “beam” will be used in referenceto the output of a light emitter such as an LED. The beam will notnecessarily be collimated or confined to a single direction, but may bedivergent, convergent or of any suitable shape. Similarly, “light”should be understood to broadly mean electromagnetic radiation and isnot confined to the visible portion of the electromagnetic spectrum.

In another aspect the present invention provides a particle detectionsystem including; at least one light source adapted to illuminate avolume being monitored, said illumination including a pulse trainincluding a plurality of pulses, said pulse train being repeated with afirst period; a receiver having a field of view and being adapted toreceive light from at least one light source after said light hastraversed the volume being monitored and being adapted to generatesignals indicative of the intensity of light received at regions withinthe field of view of the receiver, said receiver being configured toreceive light from the at least one light source in a series defined byan exposure time and receiving frame rate; a processor associated withthe receiver adapted to process the signals generated by the receiver,wherein the pulses with the pulse train emitted within each plurality ofpulses has a temporal position that is related to the receiving framerate.

A pulse in the pulse train can preferably have a duration about half theexposure time. Preferably the period of repetition of the pulse train issubstantially longer than the period between temporally adjacent frames.The frame rate is in any one of the following ranges: 100 fps-1500 fps,900 fps-1100 fps, 500 fps to 1200 fps. Most preferably the frame rate isabout 1000 fps.

The duration of a pulse is preferably between 1 μs and 100 μs. Mostpreferably the duration of a pulse is about 50 μs.

The exposure time will typically be between 2 and 200 μs. Preferably theexposure time is about 100 μs.

The pulse train can include at least one synchronisation pulse.Preferably it includes 2. The pulse train can include at least one pulseat a first wavelength. the pulse train can include at least one pulse ata second wavelength. The pulse train can include at least one datapulse.

The frame rate and temporal spacing between each of the pulses areselected such that, in at least a first time period, there is changingphase difference between them. the frame rate and temporal spacingbetween each of the pulses are selected the temporal spacing betweeneach of the pulses is such that each of the pulses in a pulse trainsubstantially fall within a respective exposure.

In another aspect of the present invention there is provided a method ina particle detection system including; at least one light source adaptedto illuminate a volume being monitored, a receiver having a field ofview and being adapted to receive light from at least one light sourceafter said light has traversed the volume being monitored and beingadapted to generate a series of frames indicative of the intensity oflight received at regions within the field of view of the receiver, anda processor associated with the receiver adapted to process the signalsgenerated by the receiver, and provide an output; said method including:determining a number of light sources from which the receiver isreceiving light.

The method can further include: analysing a plurality of frames outputby the receiver to determine the number of light sources.

The method can further include: operating the receiver at a high framerate during the step of determining the number of light sources; andsubsequently operating the receiver at a second lower frame rate.

The method can further include: analysing a plurality of frames from thereceiver to identify regions having relatively high variation inreceived light level between frames to identify candidate positionswithin the field of view of the receiver.

The method can further include: comparing the variation in receivedlight levels for a position between frames to a threshold.

The method can further include: attempting to synchronise the receiverto a predetermined transmission pattern expected from a transmitter fora candidate position, and in the event synchronisation is successfuldetermining the candidate position is receiving light from atransmitter.

The method can further include: attempting to synchronise the receiverto a predetermined transmission pattern expected from a transmitter fora candidate position, and in the event synchronisation is unsuccessfuldetermining the candidate position is not receiving light from atransmitter.

The step of attempting to synchronise the receiver to a predeterminedtransmission pattern can include: capturing a plurality of at leastpartial frames including the candidate location; comparing the receivedframes to an expected pattern of received light corresponding to a pulsetrain emitted by a transmitter; attempting to synchronise to thereceived pattern using a phase locked loop.

The step of comparing the received frames to an expected pattern ofreceived light corresponding to a pulse train emitted by a transmitter;can include determining a reference level of received light representinga time when no pulse is received for the candidate position; comparing alight level received from each pulse to the reference level and if thedifference exceeds a predetermined threshold, determining a pulse isreceived.

The step of comparing the received frames to an expected pattern ofreceived light corresponding to a pulse train emitted by a transmitter;can includes determining whether a series of pulses corresponding to anexpected pattern is received.

The method can further include: comparing the determined number of lightsources with a predetermined number of light sources; and in the eventthat the determined number does not match the predetermined numbereither: repeating the determining step; or signalling a fault.

In order to more clearly explain each of the aspects of the presentinvention and their implementation, these aspects have each beendescribed in relation to separate embodiments. A person skilled in theart will readily understand how to combine two or more of suchembodiments into an implementation of the invention. Thus it should beunderstood that the invention disclosed and defined in thisspecification extends to all alternative combinations of two or more ofthe individual features and aspects mentioned or evident from the textor drawings. All of these different combinations constitute variousalternative aspects of the invention.

Throughout this specification the term “beam” will be used in referenceto the output of a light emitter such as an LED. The beam will notnecessarily be collimated or confined to a single direction, but may bedivergent, convergent or of any suitable shape. Similarly, “light”should be understood to broadly mean electromagnetic radiation and isnot confined to the visible portion of the electromagnetic spectrum.

As used herein, except where the context requires otherwise, the term‘comprise’ and variations of the term, such as ‘comprising’, ‘comprises’and ‘comprised’, are not intended to exclude further additives,components, integers or steps.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present invention will now be described,by way of non-limiting example only, with reference to the accompanyingdrawings, in which:

FIG. 1 illustrates a conventional beam detector;

FIG. 2 illustrates a beam detector capable of implementing an embodimentof the present invention;

FIG. 3 illustrates a beam detector capable of implementing an embodimentof the present invention;

FIG. 4 illustrates a scenario in which a reflection may be caused in abeam detector;

FIG. 5 illustrates a close-up view of a receiver in a beam detector madein accordance with an embodiment of the present invention;

FIG. 6 illustrates a beam detector set-up made in accordance withanother embodiment of the present invention;

FIG. 7 illustrates beam detector arrangement made in accordance withanother embodiment of the present invention;

FIG. 8 illustrates another embodiment of the beam detector made inaccordance with the present invention;

FIG. 9 illustrates schematically an embodiment of the present inventionin which the polarisation state of the transmitter and receiver arealigned;

FIG. 10 illustrates schematically an embodiment of the present inventionwith orthogonally arranged polarisation states at the transmitter andreceiver;

FIG. 11 illustrates an embodiment of the present invention in which twoorthogonally polarised beams are transmitted to a polarisation sensitivereceiver;

FIG. 12 illustrates an embodiment of the present invention with atransmitter emitting a single polarised beam to be received by twoorthogonally polarised receivers;

FIG. 13 illustrates a plan view of a volume monitored by a particledetection system operating according to an embodiment of the presentinvention;

FIG. 14 illustrates a cross sectional view through a volume of FIG. 13showing the receiver and one transmitter of that system;

FIG. 15 illustrates a schematic view of a receiver used in an example ofthe embodiment of the present invention;

FIG. 16 shows a schematic representation of a transmitter used in anembodiment of the present invention;

FIG. 17 shows diagrammatically a smoke detector and mounting arrangementaccording to the invention;

FIG. 18 shows a cross sectional side view of the smoke detector shown inFIG. 17;

FIG. 19 shows a side view of another embodiment of smoke detectorapparatus according to the invention;

FIG. 20 shows a plan view of another embodiment of smoke detectorapparatus according to the invention;

FIG. 21 shows a diagrammatic illustration of a further embodiment ofsmoke detector apparatus according to the invention;

FIG. 22 shows a cross sectional view through a component of a smokedetector made in accordance with an alternative embodiment of thepresent invention;

FIG. 23 is a schematic diagram of a beam-detector assembly having afirst module and a second module, the assembly being powered up when thetwo modules are assembled;

FIG. 24 is a perspective view of a transmitter, in accordance with anembodiment of the present invention;

FIG. 25 is a close up perspective view of the brake shoe and spindle ofthe transmitter of FIG. 24;

FIG. 26 is a perspective cutaway view of the receiver of FIG. 24;

FIG. 27 is a perspective view of a receiver in accordance with anembodiment of the present invention;

FIG. 28 is a close up perspective view of the brake shoe, lever arm andspindle of the transmitter of FIG. 27;

FIG. 29 illustrates a plot of received light at two wavelengths in abeam detector according to an embodiment of the present invention;

FIG. 30 shows a plot of the gain and corrected output when implementinga method according to an embodiment of the present invention;

FIG. 31 shows the received light level in two wavelength bands in anembodiment of the present invention; and

FIG. 32 shows the corrected output level and adjusted gain levels whenimplementing methods according to an embodiment of the present inventionin the conditions described in FIG. 31.

FIG. 33 illustrates a particle detection system incorporating a lightsource in accordance with an embodiment of the invention;

FIG. 34 illustrates the light source of FIG. 33 when partiallyobstructed by a foreign body;

FIG. 35 illustrates the light source of FIG. 33 when obstructed bysmoke;

FIG. 36 illustrates an alternative embodiment of the light sourcedepicted in FIGS. 33 to 35;

FIG. 37 illustrates a particle detection system incorporating a lightsource in accordance with an alternative embodiment of the invention;

FIG. 38 illustrates the light source of FIG. 37 when partiallyobstructed by a foreign body;

FIG. 39 illustrates an alternative embodiment of the light sourcedepicted in FIGS. 37 and 38;

FIG. 40 illustrates an optical subsystem usable in an embodiment of thepresent invention;

FIGS. 41 and 42 illustrate light sources in accordance with furtherembodiments of the invention;

FIGS. 43 and 44 illustrate the effect of modifying the beam width of alight source used in a particle detection system; and

FIGS. 45 and 46 illustrate an advantage of having different spatialprofiles for light in different wavelength bands of emitted light usedin a particle detection system;

FIG. 47 illustrates a light emitter usable in a first embodiment of thepresent invention;

FIG. 48 illustrates further detail of light emitter usable in anembodiment of the present invention;

FIG. 49 illustrates a further embodiment of a light emitter usable in anembodiment of the present invention;

FIG. 50 is a schematic block diagram illustrating a circuit usable in anembodiment of the present invention;

FIG. 51 is a plot illustrating the operation of the circuit of FIG. 50;

FIG. 52 is a schematic block diagram illustrating a second circuitusable in an embodiment of the present invention;

FIG. 53 is a plot illustrating the operation of the circuit of FIG. 52.

FIG. 54 illustrates a schematic representation of a light source of abeam detector employing an embodiment of the present invention;

FIG. 55 illustrates a schematic representation of a light source of abeam detector employing an embodiment of the present invention;

FIG. 56 illustrates a schematic representation of a light source of abeam detector employing an embodiment of the present invention.

FIG. 57 illustrates a room in which a particle detection systemaccording to an embodiment of the present invention is installed;

FIG. 58 shows a flow chart of one embodiment of process that may beimplemented to install a beam detector operating in accordance with anembodiment of the present invention.

FIG. 59 shows a flow chart of one embodiment of a process that may beperformed by a controller of a beam detector according to an embodimentof the present invention after installation;

FIG. 60 shows a flow chart of another embodiment of a process that maybe performed by a controller of a beam detector according to anembodiment of the present invention following installation;

FIG. 61 illustrates schematically part of a transmitter according to anembodiment of the present invention;

FIG. 62 shows a second embodiment of the transmitter illustrated in FIG.61;

FIG. 63 illustrates exemplary attenuators able to be used with anembodiment of the present invention;

FIG. 64 is a timing diagram illustrating graph of transmission power andcorresponding receiver state illustrating another embodiment of thepresent invention;

FIG. 65 illustrates schematically a particle detection system employinga test filter in accordance with an aspect of the present invention;

FIG. 66 illustrates an exemplary test filter made in accordance with anembodiment of the present invention;

FIG. 67 is a plot of the transmission spectrum of a filter made inaccordance with an embodiment of the present invention;

FIG. 68 to FIG. 75 illustrates various embodiments of filters made inaccordance with an aspect of the present invention.

FIG. 76 illustrates schematically a particle detection system made inaccordance with an embodiment of the present invention;

FIG. 77 illustrates an exemplary receiver made in accordance with anembodiment of the present invention;

FIG. 78 illustrates a further illustrative embodiment of a lightreceiver according to the present invention;

FIG. 79 illustrates a further light receiver made in accordance with anembodiment of the present invention;

FIG. 80 illustrates a fourth embodiment of the light receiver made inaccordance with an embodiment of the present invention.

FIG. 81 is a schematic representation of a beam detector that utilisesan embodiment of the present invention;

FIG. 82 is a schematic representation of the beam detector representedin FIG. 81, showing a different transmitter position;

FIG. 83 is a schematic diagram depicting one embodiment of a diffusingmeans, of an embodiment of the present invention where the transmitteris sufficiently far away that the beam rays entering the lens areessentially parallel;

FIG. 84 is a schematic diagram depicting another embodiment of thediffusing means of the present invention;

FIG. 85 illustrates a further embodiment of an aspect of the presentinvention;

FIGS. 86 through 89 illustrate multiple wavelength filter arrangementswhich are able to be used in an embodiment of the present invention,such as that illustrated in FIG. 85.

FIG. 90 is a schematic illustration of a fire alarm system which may beadapted to operate in accordance with an embodiment of the presentinvention;

FIG. 91 illustrates a schematic block diagram of a receiver component ofbeam detector according to an embodiment of the present invention; and

FIG. 92 illustrates an exemplary pulse train used in an embodiment ofthe present invention.

FIG. 93 illustrates schematically an environmental monitoring system inaccordance with a first embodiment of the present invention;

FIG. 94 illustrates a second embodiment of an environmental monitoringsystem in accordance with a second embodiment of the present invention;

FIG. 95 illustrates schematically a light source able to be used in anembodiment of the present invention;

FIG. 96 illustrates a system made in accordance with a furtherembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 4 illustrates a beam detector of the type described above. The beamdetector 100 includes a transmitter 102 and a receiver 104. The beamdetector 100 is set-up to detect particles in a volume 101, which may bea room for example. The transmitter 102 emits a diverging beam of lightover a field of illumination defined by lines 106. The beam of lightincludes a direct illumination path 108 which arrives without reflectionat the receiver 104. Within the field of illumination 106 of thetransmitter 102 some rays will arrive at the receiver 104 by a reflectedpath, e.g. path 110 which reflects off the ceiling 112 defining thevolume 101. The present inventors have determined that if certainconditions are fulfilled, the presence of the reflected beam 110 can beignored. For example, if the received beam satisfies minimum receivedintensity requirements; and, in the event that the beam includesdistinguishable characteristics, e.g. wavelength components and/orpolarisation states, that the received beam possesses the predeterminedcharacteristics. In some cases it is relevant whether the beam which isused for detecting particles is the direct beam 108 or the reflectedbeam 110, for example, in a multiple wavelength system, it may be thatthe surface finish of the ceiling 112 is such that light in onewavelength band will be reflected more completely than light in a secondwavelength band. In the event that these wavelength bands coincide withwavelength bands transmitted by the transmitter 102 that are used forparticle detection by the receiver 104, a differential measure ofreceived light intensity in the two wavelength bands will behavedifferently in the reflected light path 110 than in the direct lightpath 108. Accordingly, in this case, it is necessary to correctlyidentify the direct light path beam 108.

FIG. 5 illustrates one mechanism for determining a direct beam from areflected beam in such a system. In FIG. 5 corresponding features willbe numbered with the same reference numerals as FIG. 4. FIG. 5illustrates a close-up view of the receiver 104 of the beam detector 100showing a reflected beam 110 and a direct beam 108. FIG. 5 also showsthe detail of the sensor 200 of receiver 104. In this embodiment, thelikelihood of distinguishing the direct beam 110 from the reflected beam110 is improved by providing the light receiver 104 with a sensor havinga high spatial resolution. As described above, the sensor 200 of thereceiver 104 includes a multiplicity of sensing elements 202 which canindependently detect received light intensity at distinct spatialpositions. In FIG. 5, by providing a high resolution sensor 200 it canbe seen that a group of pixel 208 are illuminated by a direct beam 108and a separate and distinct group of sensor elements 210 are illuminatedby the received reflected beam 110. If the sensor element size wassubstantially larger it would not be possible to resolve these tworeceived beams into distinct groups of sensor elements. In aparticularly preferred form, the spatial resolution of the light sensoris particularly high in the direction of a plane defined by the directbeam and the reflected beam.

In most embodiments the controller of the beam detector can beconfigured to determine which of the spots, e.g. 210 or 208 has thehighest intensity, and to use the highest intensity beam for particledetection. Typically, the brightest received beam will correspond to thedirect ray 108. In an extreme case, there may be no sufficientdiscernable difference between intensity of the two received lightbeams. In this case, the beam which arrives at the receiver furthestfrom the reflecting surface is preferably selected as the direct beam asthe other beam i.e. a beam nearer the reflective surface, is more likelyto be the reflected ray.

In one exemplary embodiment, the resolution of the image sensor is640×480 pixels.

FIG. 6 shows a further beam detector installation made in accordancewith an embodiment of the present invention. In this case, beam detector300 includes a transmitter 302 and a receiver 304. The operation of thebeam detector is substantially identical to those described elsewhereherein. However, the beam detector installation additionally includestwo baffles 306 and 308 attached to the reflecting surface 310. Thebaffles 306 and 308 extend outwardly from the reflecting surface 310towards the direct beam path 312 and serve to intercept reflected beampaths which could potentially reach the receiver 304. The number andlength of the baffles can be chosen to suit the particular installationand may be positioned to extend almost entirely down to the direct beam312. Alternatively, if accurate positioning is possible, a relativelyshort baffle can be used if an accurate position of the reflected beamcan be determined. Another option involves a longer baffle having anaperture accurately positioned so that the direct beam 312 passestherethrough. As will be appreciated, the same effect can be achieved byplacing the transmitter and receiver in close proximity to an existingstructure which will act like a baffle, for example, in a warehouse typeinstallation in which the warehouse has a number of horizontallyextending ceiling support beams placed beneath the ceiling, thetransmitter receiver may be located slightly below the beams such thatthe beams in effect operate as baffles to prevent interference fromreflections off the ceiling's surface.

FIG. 7 illustrates a further embodiment of the present invention. Thisembodiment shows a beam detector set-up 350 comprising a transmitter 354and a receiver 356. The transmitter 352 emits a beam or beams of lightover a predetermined illumination field and as discussed with theprevious embodiments, both direct beams 358 and reflected beams 360 mayarrive at the receiver 356. In this embodiment, the receiver isconfigured such that it has a field of view 8 that is relatively narrowin the direction of the reflection and as such the receiver 356 isunable to ‘see’ the reflecting surface 362. If the receiver 356 cannotsee the reflective surface 362, the only light path to the receiver fromthe transmitter 354 which will produce a sufficiently strong signal tobe discernable will be the direct beam 358. Similarly, the field ofillumination of the transmitter 354 can be confined such that it doesnot illuminate the reflective surface 362. Typically in beam detectorinstallations the reflective surface will be a ceiling of a room beingmonitored. In this case, the field of view of the receiver 356 and/orthe field of illumination of the transmitter 354 will need to beconstrained in the vertical direction. Suitable fields of view for fieldof illumination will have an angle of divergence of between 0° and 5°.However, this requirement will differ depending on the geometry of thesystem. Clearly a system with a long distance, say a 100 meters betweenthe transmitter and the receiver will require a very narrow angle ofbeam divergence or viewing angle to achieve this outcome. However, in anembodiment with only 3 meters between the transmitter and the receiver amuch wider angle of illumination and field of view is acceptable.Proximity to the reflective surface will also influence the requiredangles to achieve the aforementioned results.

FIG. 8 shows a further embodiment of a beam detector made in accordancewith an aspect of the present invention. In this embodiment, the beamdetector 500 includes a transmitter 502 and a receiver 504. Thetransmitter 502 includes two light emitters 502A and 502B. Each lightemitter 502A, 502B emits a beam or beams of light over its respectivefield of illumination and may direct a direct beam 508 and a reflectedbeam 510 which arrive at the receiver 504. The two light emitters 502Aand 502B are configured to be actuated in predetermined illuminationsequence such that the source of a received beam, i.e. which emitter itcame from, can be determined by analysing the light received at thereceiver 504. In this embodiment, the light which arrives at thereceiver 504 via the direct light path 508 will form an image 514A onthe receiver sensor (not shown), whereas the light received at thereceiver by the reflected light path 510 will form an image on thesensor of the receiver 504 such as that shown at 514B. As will beappreciated, the image formed on the receiver in the two cases (i.e.direct and reflected) differ from each other in that one is a mirrorimage of the other. The directly formed image 514A preserves therelative positioning of the two light sources 502A and 502B whereas, inthe reflected image 514B, the positions of these two sources 502A and502B are flipped in the plane containing the reflected beam andreceiver. Accordingly, by analysing the received images, it is possibleto determine which pair of received beams corresponds to the direct beampath 508 and which pair correspond to the reflected beam path 510. Inother embodiments of the present invention the two light sources 502Aand 502B can be light emitters with different wavelength or polarisationcharacteristics, rather than being illuminated with different modulationpatterns.

As will be appreciated by those skilled in the art any shapedarrangement of light images on the transmitter. For example, a twodimensional ray of distinguishable light emitters can be incorporatedinto a transmitter to allow determination of the direct or reflectedbeams from any reflective surface in any orientation with respect to thebeam.

Turning now to FIG. 9, a beam detection system 1100 is illustrated. Thebeam detection system can be of any of the types described above andincludes a transmitter 1102 and a receiver 1104. The transmitter canemit any number of beams of light in any one or more transmission bands.The beam or beams emitted by the transmitter 1102 are received by thereceiver 1104. In this embodiment, the transmitter is arranged totransmit polarised light (e.g. vertically polarised light). The receiver1104 is adapted to receive only light having the same polarisation asthat transmitted.

Polarisation of the transmitter can be achieved in a wide variety ofways including by using an inherently polarised light source such as alaser diode or by placing a polarising filter in the beam path of arandomly (or otherwise) polarised light source. Similarly, thepolarisation sensitivity of the receiver can be determined by theinherent characteristics of the receiver or by the placement of one ormore polarising filters before the sensor elements of the receiver.

In this example, nuisance light such as ambient sunlight which isgenerally not polarised or is randomly polarised will be substantiallyrejected by the receiver, whereas all of the transmitted beam (less thatproportion extinguished by particles and objects between the transmitterand receiver) will be received by the receiver 104.

FIG. 10 illustrates a similar system to the FIG. 9. The system 1200 inFIG. 10 includes a transmitter 1202 which emits a light beam 1206 thatis received by the receiver 1204. In this example, the transmitter ispolarised in a first direction (e.g. vertically polarised) and emits atleast one polarised beam 1206. The receiver 1204 is arranged to receivelight in a polarisation orthogonal to beam transmitted by thetransmitter 1202. In this case, the receiver 1204 is adapted to receivehorizontally polarised light. Such a polarisation offset presents abenefit in that large particles, like dust, in the path of the beam 1206may be distinguished from small particles, like smoke. This is becauselarge particles like dust tend to forward scatter light with randompolarisation and thus increase the cross-polarised component of lightreceived at the receiver 1204.

Combinations of the two embodiments described in FIGS. 9 and 10 can beincorporated into a particle detection system. Turning firstly to FIG.11 the system 1300 includes a transmitter 1302 and a receiver 1304. Thetransmitter 1302 is adapted to emit light beams 1306A and 1306B. A firstof these two light beams 1306A is arranged to be emitted with a firstpolarisation state whereas the second beam 1306B is emitted with anorthogonal polarisation state. The receiver 1304 is arranged to receivelight in a single polarisation only e.g. in the first polarisationstate. Accordingly, as will be appreciated both techniques described inrelation to FIGS. 9 and 10 may be applied in the same receiver.Preferably, the transmitter 1302 is arranged to generate beams 1306A and1306B alternately so that the two polarisation state beams arrive atdifferent times at the receiver 1304.

An alternate system is illustrated in FIG. 12. In this system the beamdetector 1400 comprising a transmitter 1402 and a receiver 1404. Thetransmitter 1402 is configured to emit a vertically polarised beam 1406.The receiver 1404 is adapted to be able to resolve light received inplurality of polarisation states e.g. in vertical polarisation state ora horizontal polarisation state. This can be achieved by having aplurality of adjacent light receiving elements having differentpolarisations which are operated either concurrently or alternately. Inthis example, a beam splitting component 1408 is provided prior to thereceiver elements to direct beams to each of the receivers.

As will be appreciated by those skilled in the art references thespecification to vertical and horizontal polarisation have been selectedfor convenience only and any polarisations may be used. Moreover, forconvenience of description orthogonal polarisation states have beenselected to illustrate the present invention. However, the presentinvention should not be taken as being limited to polarisation stateswhich are either aligned or orthogonal to one another. Other angularoffsets between polarisations are possible. Those skilled in the artwill be able to determine the appropriate calculations to perform toaccount for this variation.

One way of achieving variation in polarisation states for a receiver ortransmitter is to provide mechanical means for placing polarisingfilters in the light path. For example, a solenoid can be used as anactuator to move a reciprocating polarising filter into and out of thebeam path. Alternatively a rotating filter mechanism can be employedwhich has plurality of differently polarised filters around a wheel likestructure. By rotating the wheel like structure through the light pathdifferent polarisations can be achieved over time. Other mechanicalarrangements are also possible, for example, the light emitting elementof the transmitter 402 could be physically rotated about an axis ascould the one or more sensors of the receiver. Other mechanicalarrangements will be apparent to those skilled in the art.

FIG. 13 illustrates a plan view of a room 400A in which is installed abeam detector system 402A according to an embodiment of the presentinvention. The beam detection system includes a single receiver 404Aconfigured to monitor eight transmitters 406A, 406B through 406H. Eachof the transmitters 406A to 406H is adapted to transmit light with ahorizontal angle of illumination of a degrees. It is also adapted totransmit light with a vertical angle of illumination of β degrees asshow in FIG. 14. Similarly the field of view of the receiver 404Adiffers in its horizontal and vertical extent. In this example, thereceiver 404A is adapted to receive light over a viewing angle of γdegrees and vertical viewing angle of δ degrees. In a preferred form ofthe present invention the horizontal angle of illumination of thetransmitters 406A to 406H is wider than their vertical angle ofillumination β. Similarly, the receiver 404 has a wider horizontal fieldof view than it does vertical field of view.

The differential fields of view and fields of illumination of thereceiver and transmitter respectively are chosen to account foralignment tolerances in the typical installation. For example, in mostinstallations such as that illustrated in FIG. 13 the transmitters 406Athrough 406H will typically be installed at the same height as eachother and the receiver 404A will be mounted in a plane parallel to thetransmitters 406A to 406H. Accordingly, when the image of thetransmitters 406A through 406H is received on the light sensor of thereceiver 404A they will tend to align on the light sensor. Accordingly,a relatively narrow field of view can be tolerated in the verticaldirection for the receiver 404A. However, as will be apparent from FIG.4 a very wide horizontal field of view is required by the receiver 404A.Similarly, horizontal alignment of the transmitters 406A to 406H is moredifficult to achieve than vertical alignment in most installations. Thisis typically because the range of movement in the vertical plane is morelimited and typically walls of a building are relatively parallel inalignment. For this reason an installer may get away with mounting thetransmitter and receiver such that their field of view is orthogonal tothe plane of the surface on which they are mounted and this will achievea suitably accurate vertical alignment. However, this may not be thecase with horizontal alignment as the angle of illumination of the lightsources and angle of reception of the light receiver will vary from theorientation of the surface on which they are mounted due to the geometryof the system being installed. Thus providing an ability for horizontalalignment is necessary and the horizontal field of view of the receiverand horizontal beam width of the transmitters is advantageouslyrelatively wide.

For example, a receiver may be adapted such that its horizontal field ofview approaches 90 degrees while its vertical field of view is onlyaround 10 degrees. Similarly, a transmitter may be configured such thatits horizontal beam width is around 10 degrees whereas its vertical beamwidth may be between 3 and 5 degrees.

In order to achieve different horizontal and vertical beam divergencesor viewing angles either a transmitter or receiver may be fitted with anoptical system including an anamorphic lens.

FIG. 15 illustrates an exemplary configuration of a receiver such asthat described in connection with FIG. 13.

The receiver 420 includes a multi segment light sensor 422 which iscoupled to a video readout and processing subsystem 424. The lightreceiver 920 includes an optical arrangement 426 comprising e.g. aplurality of lenses or other optical components e.g. mirrors, forfocusing received light on the sensor array 422. In a preferred form,the anamorphic lens is arranged to provide a substantially differenthorizontal and vertical field of view for the receiver.

FIG. 16 illustrates a transmitter 700 which includes at least one lightemitter 702 adapted to emit one or more beams of light in one or morewavelength bands. The transmitter 700 includes control circuitry 704which is powered by a power source 706 which may, for example be abattery. The light emitter 702 emits a beam of light 708. This beam oflight is shaped into a particular dispersion pattern or beam shape by anoptical arrangement 710. As described above, the optical arrangement 710can include one or more anamorphic lenses.

As will be appreciated by those skilled in the art differentinstallations will have different geometrical limitations placed on themand requirements. Accordingly, the present invention should not beconsidered as being limited to the case where the beam shape of atransmitter e.g. 406 or a receiver e.g. 404 is defined by its verticalor horizontal angles. Rather, the present invention extends to systemsin which either or both of the beam width of a transmitter or angularextent of a receiver is different in any two directions whether they areorthogonal with each other or not and whether they are alignedvertically and horizontally or not.

Irrespective of whether the particle detection system is of the typedepicted in FIG. 1, FIG. 2 or FIG. 3 of the drawings, or of a differenttype, such as that disclosed in PCT/AU2004/000637, PCT/AU2005/001723 orPCT/AU2008/001697 the alignment of the components of the system, eg alight source with the target and the reflection of an emitted beam backto the receiver is important. As mentioned above, there can be asignificant distance between the source and the target, thus aligningthe light source accurately with the target can be difficult. For thisreason it is preferable that an adjustable mounting arrangement isprovided which allows the direction of the light source (and/ortarget—if it is not retro-reflective) to be varied, both at the time ofinstallation, and in the event that movement of the light source and/orthe target from its installation position occurs.

FIG. 17 depicts one embodiment of an alignment beam arrangement whichwill assist in the alignment of the optical components of a particledetector. The device depicted in FIG. 17 is of a type discussed abovewith respect to FIG. 2, but the smoke detector can take variousdifferent forms. As shown, the smoke detector 2200 includes the lightsource 2202 and a receiver 2204. In addition, the smoke detector 2200includes a visual alignment device 2230 of the type adapted to generatean alignment beam 2242 which is axially aligned with the light source2202 but which is visually observable. The beam 2242 will project ontothe target 2206 located some distance away from the smoke detector 2200.

The smoke detector 2200 is provided with a mounting means in the form ofa circular plate 2232 which in use will be mounted by screws or the liketo a support surface in order to fix the smoke detector 2200 at aappropriate elevation to that support surface. An articulated connection2234 is provided between the mounting plate 2232 and the smoke detector2200. The articulated connection can take various forms, which willallow the alignment of the detector to be varied, but being lockable inthe selected orientation. A friction lock arrangement is possible, orsome form of screw tightening arrangement might be used.

As shown in FIG. 18, the articulated connection 2234 comprises a cup2236 and ball 2238, the ball being able to rotate within the cup. Theball is captively held by the cup so as to allow the smoke detector 2200to be tilted relative to the support plate 2232, thereby allowing theincident light 2210 to be directed precisely to the target 2206 somedistance away. A grubscrew 2240 is provided for locking the ballrelative to the cup. Other forms of locking the ball in the cup arepossible, including, for example a friction fit.

As mentioned, the alignment beam 2242 is used to facilitate thealignment of the incident light 2210 with the target. Thus, thealignment beam 2242, which would typically comprise a laser beam, isparallel to the incident light 2210. An operator would thus be able topoint the alignment beam 2242 at the target or just adjacent to thetarget to thereby ensure that the incident light 2210 (which istypically not visible) is aimed centrally at the target. Once theincident light 2210 is aimed at the centre of the target, the grubscrew2240 will be tightened, thereby locking the ball 2238 within the cup2236. This will ensure that the smoke detector 2200 is optimally alignedand calibration of the system can then take place in the mannerdescribed herein.

FIG. 19 of the drawings depicts a manner of securing the smoke detector2200 in a selected operable position. In this embodiment, the smokedetector 2200 forms an optical module that includes an elongaterecess/passage 2244 forming an engagement feature. The recess/passage2244 has one open end 2247 and is arranged so that the axis of therecess/passage projects toward the target when the smoke detector 2200is in alignment with it. The grubscrew 2240 used for locking the ball2238 within the cup 2236 is accessible along the passage 2244 extendingthrough to the front side 2246 of the detector housing 2200. The passage2244 is configured to receive the shaft 2248 of an alignment tool 2250.The alignment tool 2250 has a driver 2252 on one end thereof and ahandle 2254 on the other end thereof. The handle 2254 has a recess 2256in the rear end thereof into which a laser 2258 has been inserted. Theshaft 2248 is a close sliding fit with the passage 2244 such as when theshaft is located in the passage 2244 the laser beam 2242 from the laser2258 is axially aligned with the light source 2202 and/or receiver 2204,as discussed above.

In this embodiment the shaft 2248 and the passage 2244 each have acomplementary cylindrical shape. Of course the person skilled in the artwill appreciate that other arrangements are possible, for examplepassage 2244 may have a square profile, the side dimension of the squarecorresponding to the diameter of the shaft 2248.

The installer, using the tool 2250 depicted in FIG. 19, will thus insertthe shaft 2248 into the passage 2244 and then manipulate the housing2200 whilst observing the visible alignment beam 2242 at a remotetarget. When the housing is correctly aligned, the handle 2254 will berotated with driver head 2252 engaged with the grubscrew 2240 to therebytighten the grubscrew 2240 and lock the cup and ball together. Oncelocked together in this way, the technician installing the equipmentwill check that the laser beam 2242 which is still correctly alignedwith the target, and if so, will know that the smoke detector iscorrectly orientated. Clearly, at any time in the future, such aswhenever the equipment is to be maintained or serviced, the orientationof the unit can be checked by simply inserting the shaft of the tool2250 into the passage 2244 and checking, once again, whether the laserbeam 2242 is correctly aligned with the target on the remote location.

In this embodiment, the driver 2252 is shown as a screw driver head, butclearly if the grubscrew has some other form of engagement formation,such as an Allen key socket, then the driver 2252 will be in theappropriately sized six sided Allen key configuration.

Whilst FIG. 19 depicts a tool having a laser installed therein foralignment purposes, it will, of course, be possible simply to insert alaser 2258 into the passage 2244 to assist with alignment of the housingrelative to the remote target.

FIGS. 17 to 19 depict an arrangement in which the beam is alignedparallel to the incident light beam but this is not the only possiblearrangement. For example, the housing may have a plurality of laserreceiving sockets therein angled to the incident beam in a configurationwhich assists in the set up and orientation of the smoke detectorrelative to a remote target or area of interest. For example, where thesmoke detector is of the form discussed above with reference to FIG. 3,then it may be desirable to have a laser beam which also indicates thefull arc 2622 of the light source illumination. Clearly it would bepossible to include a socket in the housing 2200 at an angle to theincident beam which will correspond to the full arc of the light sourceillumination.

FIG. 20 depicts diagrammatically a housing having three sockets 2249,each of which is adapted to receive a tool 2250 shown in FIG. 19 so asto enable the installation technician to correctly align the housing foroptimal performance. The lateral two sockets 2249 are preferably alignedrelative to the arc of visible light which the video camera is able todetect, and the central socket will be used to align the centre of thevideo camera with the target 2206 at the remote location.

FIG. 21 depicts a further embodiment of the invention. In thisembodiment the visual alignment device 2260 includes a shaft 2262 whichin turn is mounted in a socket of the smoke detector housing 2264 andwill be aligned in fixed orientation to the optical components mountedin the housing 2264. A video camera 2266 is mounted in a handle portion2268 at the end of the shaft 2262. The video camera will preferably bebattery powered, and is adapted to generate an image of a target at alocation remote from the housing 2264. The video camera is preferablyprovided with a telescopic lens.

The image viewed by the video camera is preferably transmittedwirelessly to a receiver unit 2270 which includes a screen 2272 on whichthe image of the remote target is displayed. The image may also includea sighting symbol or device 2274 which may be in the form ofcross-hairs, or some other form of alignment assisting sighting device,such as a grid pattern or the like.

Clearly, when the housing is moved the field of view of the video cameraand hence image generated via the video camera will move on the screen,and the technician doing the alignment of the smoke detector will beable to correctly orientate the housing by viewing the image on thescreen. Since the video camera is aligned in a fixed relative alignmentto the optical components of the smoke detector, once the image on thescreen is correctly aligned with the intended target, the technicianwill know that the optical components are correctly aligned. Thereceiver unit is preferably a hand held, battery powered computer devicesuch as a PDA or the like, showing real time images from the camera. Theconnection between the camera and the receiver will preferably bewireless, but could also be via cable.

The camera may be fitted with a wavelength dependent light filter, at awavelength that corresponds to a light source, such as a LED, or otheractive or passive light source, mounted at the target position. Thetarget light source may flash, optionally at a specific rate or pattern,so as to be readily discernable to the human eye. The pattern of flashmay also be identified by software in the camera and/or the receiver.

The software in the receiver unit and or the camera may include meansfor generating an enhanced view of the target on the display, and mayinclude surrounding images of the room or surface on which the target ismounted. The receiver unit and camera combination preferably includesmeans for generating audible sound cues and/or voice instructions to theoperator to assist in the alignment process. These instructions may bein the nature of instructions on how to move the housing so as tocorrectly align with the target, and could include audible words such as‘up’, ‘down’, ‘left’, ‘right’, ‘on target’, and the like.

It will be appreciated that, with the video camera mounted at the end ofthe shaft 2262, a small movement of the housing about articulatedconnection 2274 will move the video camera at the end of the shaftthrough a relatively wide arc. The shaft thus acts as a lever arm, withthe video camera mounted on the distal end of the arm. This increasesthe sensitivity of the alignment process, so that, provided the videocamera and optical components are in the correct relative alignment,when the video camera is correctly aligned with the target the opticalcomponents will be precisely aligned in the intended orientation.

FIG. 22 shows an alternative housing configuration for opticalcomponents made in accordance with an embodiment of the presentinvention.

In this example the component 2900 includes an electro-opticalcomponent, such as a camera or light source(s) and its associatedelectronic circuitry and optics 2904. The electro-optical component 2902is mounted in a fixed relationship with respect to the housing 2906 andis connected via fixed wiring 2908 to electrical and data connections2910.

The housing 2906 includes an aperture 2912 through which a beam of lightmay enter or exit the housing. The aperture 2912 may be open or can beclosed by a lens or window. The component 2900 also includes an opticalassembly 2914 mounted to the housing 2906. The optical assembly, in thiscase, is a mirror mounted at an angle with respect to the optical axisof the electro-optical system 2902, 2904. The mirror is used to redirectan optical signal either to or from the electro-optical system 2902,2904 and through the aperture 2912.

The mirror 2914 is mounted to the housing 2906 via an articulatedmounting means 2916. The articulated mounting means in this casecomprises a rotatable shaft mounted in a rotation friction bearing 2918which is captured in a corresponding shaped recess 2920 in the housing2906. The articulated mounting 916 includes an engagement means 2922which can be engaged from the outside of the housing 2906 using analignment tool. For example, an alignment tool described in relation tothe previous embodiments can be used.

In use, a technician installing the optical component uses the fixedmounting means to attach the housing in a fixed manner with respect to amounting surface and then adjusts the external field of view (orillumination) of the electro-optical components 2902 by adjusting theorientation of the mirror 2914 using an alignment tool. The method ofoperation of the system is substantially the same as that describedabove except that the articulated connection enables the orientation ofthe optical assembly 2914 to be changed with respect to theelectro-optical component which is mounted in a fixed relationship withthe mounting surface, rather than enabling realignment of the entirehousing with respect to the mounting surface.

FIG. 23 illustrates a beam-detector assembly 2300 which may, forexample, be a light transmitter. The assembly 2300 is constructed in twomodules. Module 2302 is a main enclosure housing a battery (notillustrated) and the electro-optical system 2306 for the unit. Theelectro-optical system 2306 may be mounted on a circuit board 2308.Module 2302 also includes a switch 2310 that, in one arrangement, isresponsive to magnetic fields. An example of such a switch is a reedswitch, which has of a pair of contacts on ferrous metal reedspositioned in a hermetically sealed glass envelope. The contacts areinitially separated. In the presence of a magnetic field the switchcloses. Once the magnetic field is removed, the stiffness of the reedscauses the contacts to separate.

Other switching devices that are sensitive to magnetic fields, such asHall-effect devices may also be used.

Module 2304 is a mounting base, which includes an actuator capable ofacting on the switch 2310. The actuator may, for example, be a magnet2312.

The modules 2302 and 2304 are transported and stored separately from oneanother or in a package where the actuator is separated from the switchby sufficient distance to prevent activation of the switch. Typically,at installation, the module 2304 is affixed to a wall 2320 or mountingsurface and the module 2302 is then attached to module 2304. It will beappreciated that there are many arrangements that enable module 2302 tobe easily and securely mounted to module 2304. For example, module 2304may have one or more tracks and, during assembly, the module 2302 may beslid along the tracks as far as a stopper. A detent means may beprovided to hold the two modules in position. Such arrangements allowthe two modules to be assembled in a predetermined orientation, thuspositioning the switch 2310 relative to the magnet 2312.

Only when the modules 2302 and 2304 are assembled is the switch 2301closed, permitting significant power consumption from the battery tobegin.

In another arrangement, module 2304 includes a plurality of magnets2312. The configuration of magnets 2312 may be used to represent an itemof information, such as identifying data for the module 2304. Theinformation may include a serial number or a loop address associatedwith the location of the module 2304. By providing a pattern of magnetson the base module 2304, the data may effectively be retainedpermanently at the location where module 2304 is attached to the wall2320. Thus, even if the module 2302 is replaced, for example after afault such as a depleted battery, the identifying data is still present.

The module 2302 may include a plurality of switches 2310 or sensorssensitive to the presence of the magnets 2312 in module 2304. Forexample, an array or predetermined pattern of reed switches may beprovided, capable of reading the identification data coded in thepattern of magnets in module 2304.

In a further arrangement, the pattern of magnets 2312 in module 2304 maybe provided on a removable device, such as a card. The card with thepattern of magnets may, for example, be inserted into the module 2304when the module is affixed to the wall 2320.

FIGS. 24 to 26 illustrate an alternative embodiment of the invention.The transmitter unit 3000 includes a housing 3200, forming an opticalmodule. The transmitter further includes a backing plate 3010, rearcasing 3020 and forward casing 3030 which together form a mountingportion 3180.

The backing plate 3010 includes screw holes through which it may bemounted to a mounting surface (not shown) such as a wall. The backingplate 3010 is attached to the rear casing 3020 with a simple,releasable, snap fit.

The rear casing 3020 and forward casing 3030 together define a partialspherical cavity in which the housing 3200 is received. The housing 3200includes a rear housing 3040 and a forward housing 3050.

Each of the rear and forward housing 3040, 3050 has a predominantlyhollow hemispherical shell like form.

The rear housing 3040 has a lip about its outer periphery. The forwardhousing 3050 a complementary lip on the interior of its outer periphery.The complementary lips are snap fitted together to define the sphericalhousing 3200. Adjacent this snap fit a small portion of the rear housing3040 projects into the forward housing 3050 and defines an annular stepthereabouts.

The outer surface of detector housing 3200 is predominantly sphericaland complementary to the spherical cavity defined by the rear casing3020 and the forward casing 3030. There is a close sliding fit betweenthe complementary spherical surfaces so that the housing 3020 may berotated to a wide range of orientations relative to the mounting portion3180 and loosely frictionally held in alignment during installation.

A forward end of the forward casing 3030 is open to expose the housing3200. In this embodiment the opening in the forward casing 3030 isshaped, and curved, to allow the housing 3200 to be articulated to awider range of angles about a vertical axis than about a horizontalaxis: typically such transmitters are wall mounted close to the ceiling,as are the corresponding receivers, it follows that generally lessadjustment is required about a horizontal axis, i.e. in the up and downdirection.

A forward end of the forward housing 3050 is truncated to define acircular opening in which a lens 3060 is carried. A circular printedcircuit board (PCB) 3070 is centrally mounted within and spans thehousing 3200. The PCB 3070 is parallel to the lens 3060 and seatsagainst the annular step defined by the rear housing 3040 projectinginto the forward housing 3050.

A light source in the form of LED 3080 is centrally mounted on a forwardsurface of the PCB 3070 and in use projects a beam of light e.g. in oneor more wavelength bands, the obscuration of which provides anindication of the presence of particles. The lens 3060 is arranged tocollimate the beam projected by the LED 3080. A battery 3090 is carriedon a rear face of the PCB 3070.

The illustrated embodiment includes a locking mechanism 3190 including aspindle 3240, a cam 3100 and a brake shoe 3110 illustrated in FIG. 25.The spindle 3240 has at its axial mid point an outwardly projectingcollar 3140.

Each of the rear housing 3040 and the forward housing 3050 include atubular recess for receiving a respective portion of the spindle 3240.The collar 3140 is captured between the rear housing 3040 and theforward housing 3050 when the rear and forward housings are snap fittedtogether. O-ring seals around the spindle fore and aft of the collar3040 limit the ingress of debris into the housing 3200 via the tubularrecesses.

A hexagonal socket 3160 is formed in a forward end face of the spindle3240. A cylindrical tubular passageway 3244 passes through the forwardhousing 3050 and provides access to the socket 3160. The socket 3160during installation of the transmitter unit receives an Allen key likefitting from the front of the transmitter unit 3000 via the passage 3244so that an installer may rotate the spindle 3240 about its axis. As willbe described, said rotation locks the housing 3200 in a selectedorientation relative to the mounting portion 3180.

The rear housing 3040 has a rearward aperture in which is carried abrake shoe 3110. The brake shoe 3110 has an outer surface 3130 which ispart spherical and aligned with the spherical outer surface of the rearhousing 3040 when in a retracted ‘articulating position’. The brake shoe3110 carries a stud 3120 on each of its sides. The studs 3120 project ashort sideways distance, i.e. in directions perpendicular to the up anddown and fore and aft directions. The studs 3120 are received withincomplementary recesses (not shown) in the rear housing 3040 and therebydefine a pivot about which the brake shoe 3110 may rotate through arange of motion. The range of motion is limited by contact between thebraking surface 3130 and the internal spherical surface defined by rearand/or forward casings 3020, 3030, and by contact with a cam 3100described below.

As illustrated in FIG. 25 the brake shoe 3110 includes a centrallongitudinal channel separating two wing portions which each carry arespective stud 3120. The brake shoe 3110 has a degree of compliance sothat the brake shoe 3110 and the rear casing 3040 may be assembled bycompressing the wing portions, to reduce the overall dimension acrossthe studs 3120, and fitting the brake shoe 3110 to the rear casing 3040so that the studs 3120 are received into the complementary recesses (notshown) formed in the rear casing 3040. Once released the wing portionsreturn to their uncompressed shape so that the studs 3120 snap into thecomplementary recesses.

The cam 3100 is carried by the spindle 3240. Of course another optionwould be for the cam to be integrally formed with the spindle asillustrated in FIG. 28. The cam 3100 includes a single lobe and isarranged to act downwardly on the brake shoe 3110 at a locationforwardly spaced from the studs 3120 (and a pivot axis defined thereby).

During installation of the receiver 3000, after aligning the housing3200, an installer accesses socket 3160 of spindle 3240 via the passage3244 with an Allen key like tool. Using the Allen key like tool torotate the spindle 3240 rotates the cam 3100, which in turn drives theforward portions of the brake shoe 3110 downwardly so that the brakingsurface 3130 frictionally engages the internal spherical surface definedby rear and forward casings 3020 and 3030. The alignment of the housing3200 relative to the mounting portion 3180 is thereby locked.

In this embodiment the lens 3060 and LED 3080 are configured to projectlight in a direction perpendicular to the plane of the lens 3060. Thepassageway 3244 is also perpendicular to the plane of the lens 3060.During installation an alignment tool, similar to those described above,may be used, wherein the alignment tool has a cylindrical shaft sizedfor a close sliding fit with the passage 3244 and includes a laserpointer arranged to project a beam coaxial with the shaft. In thisembodiment the shaft of the alignment tool terminates in an Allen keyfitting complementary to the socket 3160. During installation the toolis inserted into the passage 3244 and engaged with the socket 3160. Whenengaged, the alignment tool can be used as a lever and may bemanipulated until its projected beam is focused on a target, such as areceiver. The passage 3244 thereby provides a convenient means forproviding a visual indication of the alignment of the housing 3200. Thealignment tool may then be simply rotated about its axis to lock thehousing 3200 in the correct alignment.

As previously described, it is desirable that the power supply, in thiscase the battery 3090, is only connected (to activate the transmitter)upon installation. The collar 3140 of spindle 3240 carries at a point onits circumference a magnet 3150. The relative position of the magnet3150 and the lobe of the cam 3100 is selected so that when the brakeshoe 3110 is in an advanced, ‘braking’, position the magnet 3150interacts with a reed switch (not shown) mounted on a rear face of thePCB 3070 to close the switch and thereby connect the power supply andactivate the receiver 3000. The location of the magnet about the collar3140 relative to the lobe of the cam 3100 is selected so that when thebrake shoe 3110 is in the retracted, ‘articulation’, position the magnet3150 does not act on the reed switch, so that the reed switch remainsopen, and the receiver remains inactive.

The transmitter unit 3000 is simple to install. The receiver 3000 can besupplied as a preassembled unit—with the locking mechanism in theretracted, articulation, position so that the battery is not connectedand does not run down. The backing plate, which is attached to the rearcasing 3020 with a simple snap fit is levered off (i.e. unsnapped) andscrewed or otherwise fastened to a wall or other mounting surface. Therear casing 3020, and the remainder of the receiver 3000 attachedthereto, is then simply snapped onto the backing plate. The housing isthen aligned using the aforedescribed alignment tool and then easily andconveniently locked in said alignment and activated with a single motionof the same tool.

FIGS. 27 and 28 illustrate a further alternative embodiment of theinvention similar to the embodiment described in FIGS. 24 to 26. FIG. 28is analogous to FIG. 25 however it illustrates a receiver 3000′ useablein an embodiment of the present invention. Receiver 3000′ includes apassage 3244′ through which a spindle 3240′ may be accessed as in theprevious embodiment. This embodiment differs from the embodiment of FIG.24 in the details of the locking mechanism. The spindle 3240′ includesan integrally formed cam 3100′ arranged to act on a pivotally mountedlever arm 3210.

The lever arm 3210 has a length in the sideways direction, i.e.perpendicular to the up and down and fore and aft directions. A stud at3120′ projects forwardly from one end of the lever arm 3210. The stud3120′ is received within a complementary recess (not shown) definedwithin the transmitter housing 3200′ at which the lever arm 3210 ispivotally supported within the transmitter housing 3200′.

Short studs 3230 project in the fore and aft directions from the otherend of the lever arm 3210. The studs 3230 are coaxially aligned. A brakeshoe 3110′ including an upwardly projecting clevis arrangement embracesthe other end of the lever arm and engages with the studs 3230 topivotally connect the lever arm 3210 and brake shoe 3110′. The brakeshoe 3110′ projects downwardly from the lever arm 3210, and has a squarecross section and determinates in a part spherical braking surface3130′.

The brake shoe 3110′ is seated within and guided by a tubular throughhole (not shown), having a complementary square profile, within thetransmitter housing 3200′.

During installation of the transmitter 3000′ the spindle 3240′ isrotated, as in the previous embodiment. As the spindle 3240′ is rotatedthe cam 3100′ acts to drive the lever arm 3210 downwardly about itspivot axis (defined by the stud 3120′). The braking shoe 3110′ is inturn pushed downwardly to frictionally engage an internal surface of thefixed mounting portion 3180′.

The lever arm 3210 includes an integrally formed finger 3220 projectingdownwardly, from the end of the lever arm 3210, at an acute angle from amain body of the arm. The finger 3220 defines a curved path an outersurface of which is complementary to an interior of the transmitterhousing 3200′. The finger 3220 is dimensioned to press against saidinterior and thereby bias the lever arm 3210 to rotate upwardly aboutits pivot axis (defined by the stud 3120′). The brake shoe 3110′ isthereby biased against the cam towards a retracted, non-braking,position.

As noted previously the soiling of optical surfaces over time can causeproblems in beam detectors. To address this problem the inventors havedetermined that the system can be adapted to compensate for soiling ofthe optical system over time. FIG. 29 illustrates how the true receivedlight level i.e. the level of light arriving at the system's receiver orlight sensor decreases over time. FIG. 29 shows a plot between times t1and t2 of the true light level arriving at a sensor of a beam detectorreceiver over time. As can be seen from the plots the received lightlevel at wavelengths λ₁ and λ₂ decrease gradually over time due to thebuild up of contamination on the surfaces of the optical system of thereceiver. To compensate for the loss of sensitivity, in one embodimentof the present invention, the system gain is correspondingly increasedvery slowly over time (as indicated in FIG. 30) such that the detectedintensity λ₁ and λ₂ remains substantially stable over time.

FIG. 31 is similar to that of FIG. 30 except, as can be seen thedegradation in performance in wavelength bands λ₁ and λ₂ are different.In this embodiment, the signal at λ₂ is more greatly influenced by thecontamination of the optics than that at λ₁. In such a scenario, asystem which uses a differential, or relative value between the receivedsignals in two wavelength bands as likely to go into a false alarm stateas the separation between the received signal at wavelength λ₁ and λ₂increases. To address this problem, the gain is adjusted differently foreach wavelength, and as can be seen when the gains are adjusted, as inFIG. 30 the long term average output of the system remains substantiallyconstant.

In the examples of FIGS. 31 and 32 a smoke event 3500 occursapproximately midway between times t1 and t2. In this case, because λ₁effectively operates as a reference wavelength it undergoes a very minordrop in intensity whereas the received signal at λ₂ undergoes a verymarked drop due to λ₂'s tendency to be more strongly absorbed by smallparticles. As can be seen, because the smoke event has such a shortduration in comparison to the compensation being applied to the gainsthe long term compensation for system contamination is not affected bythe occurrence of the smoke event 3500 and the smoke event 3500 is alsoreliably detected by the system.

Referring to FIGS. 33 to 35, a light source 3300 according to anembodiment of the present invention is depicted. The light source 3300includes a housing 3302 with a transmission zone 3304 through whichlight is transmitted from the light source 3300 to a receiver 3306.

The transmission zone 3304 is in this instance located on the exteriorof the housing 3302 and provides the point at which light from withinthe housing 3302 is transmitted from the light source 3300 towards thereceiver 3306. As such, the transmission zone 3304 is accessible fromoutside the light source 3300 and may be affected by dust/dirt build up,insect/bug activity etc. The transmission zone 3304 may, withoutlimitation, be any optical surface (or part thereof), and while forillustration purposes has been depicted as protruding from the housing3302 it may, of course, be flush with or recessed within the walls ofthe housing 3302. The transmission zone 3304 may be integral with thehousing 3302 or may be a component part thereof.

In the present embodiment the housing 3302 houses a first light emitter3308, a second light emitter 3310 and a third light emitter 3312. Eachlight emitter 3308 to 3312 is an LED and emits a beam of light (3314,3316 and 3318 respectively) which is transmitted through thetransmission zone 3304 to the receiver 3306. The first light emitter3308 and third light emitter 3312 emit electromagnetic radiation in afirst spectral band, e.g. UV light (i.e. light in the ultravioletportion of the EM spectrum) of substantially equal wavelength, and assuch shall be referred to as UV emitters. The second light emitter 3310emits EM radiation in a second spectral band, e.g. IR light (i.e. in theinfrared portion of the EM spectrum) and as such shall be referred to asa IR emitter. Correspondingly, light beams 3314 and 3318 will bereferred to UV light beams and light beam 3316 will be referred to as aIR light beam.

The light source 3300 also includes a controller 3320 adapted to controloperation of the first, second and third light emitters 3308 to 3312.The controller may be housed within the housing 3302 as shown, or may beremote from the housing and control operation of the light emitters 3308to 3312 remotely.

As will be appreciated, the specific manner in which the light emitters3308 to 3312 are operated by the controller 3320 depends on theprogramming of the system. In this embodiment the controller 3320alternates operation of the light emitters 3308 to 3312 in a repeatingalternating sequence. The processing of these beams as received by thereceiver 3306 is discussed in further detail below.

The controller may also be adapted to operate one or more of the lightemitters 3308 to 3312 to send a control signal to the receiver 3306.Such a control signal may indicate status information regarding thelight source 3300, for example, convey that the light source 3300 isoperational, that the light source 3300 is malfunctioning, and/or thatthe light source 3300 battery is running out. The control signal may bedetermined by the timing and/or intensity of the light beams 3314, 3316and/or 3318 as emitted by respective light emitter 3308 to 3312.

As can be seen, the UV light emitters 3308 and 3312 are separated fromeach other which, in turn, leads to a separation of the point at whichthe UV light beams 3314 and 3318 leave the transmission zone 3304. Theseparation between the UV light emitters (and UV light beams 3314 and3318) is of sufficient distance such that if the transmission zone 3304is obstructed by a foreign body 3322 only one of the UV light beams 3314or 3318 may be obstructed. A separation of approximately 50 mm betweenthe first and third light beams 3314 and 3318 has been found suitablefor this purpose. Thus, this arrangement effectively provides aredundant light emitter in the UV band.

The term “foreign body” is used here to refer to objects or nuisanceparticles larger than dust or smoke particles or other particles ofinterest that may be present in the air. As one example, a foreign bodyobstructing the transmission zone 3304 may be an insect or bug crawlingover the transmission zone 3304.

FIG. 34 shows an example of a single UV light beam 3318 beingobstructed, with the remaining IR light beam 3314 unobstructed. In thisinstance the receiver 3306 recognises a fault condition because it onlyreceived every second expected UV pulse rather than an alarm condition.

Should this condition (i.e. the condition where only one of the UV lightbeams 3314 or 3318 is being received at the receiver 3306 or is receivedat a significantly lower level than the other due to partialobstruction) persist for a significant time, e.g. 1 minute, the receiver3306 may be programmed to interpret this as an error/malfunction withthe light source 3300 and trigger an appropriate alarm/error message.

In contrast to the obstruction shown in FIG. 34, FIG. 35 depicts thesituation where smoke particles 3324 in the air obstruct all three beams3314 to 3318. In this instance the smoke 3324 attenuates each of thelight beams 3314 and 3318 to substantially the same extent, and theusual alarm logic can be applied to determine whether an alarm or faultcondition exists.

FIG. 36 provides an alternative to the above embodiment. The lightsource 3600, similarly to the previous embodiment includes a housing3602 and a transmission zone (or window) 3604 through which beams 3614,3616 and 3618 are emitted to a receiver 3606. The operation of the lightsource 3600 is controlled by a controller 3620. UV light beams 3614 and3618 are emitted from a single UV light emitter 3626. In this case thelight source 3600 includes a beam splitter 3628 which splits the beamfrom light source 3626 such that the first and third light beams 3614and 3618 exit the transmission zone 3604 at a sufficient distance fromeach other as described above.

Turning to FIGS. 37 to 40, a further alternative embodiment of a lightsource 3700 for use in a particle detection system is provided. Lightsource 3700 includes a housing 3702 with a transmission zone 3704through which light is transmitted from the light source 3700 to areceiver 3706. The transmission zone 3704 is as described above inrelation to transmission zone 3604, however as can be seen is muchsmaller.

Housing 3702 houses first and second LED light emitters 3708 and 3710.Light emitter 3708 is a UV light emitter and emits a UV light beam 3712,while light emitter 3710 is an IR light emitter and emits IR light beam3714. The light source 3700 also includes a controller 3716 adapted tocontrol operation of the first and second light emitters 3708 and 3710.The controller may be housed within the housing 3702 as shown, or may beremote from the housing and control operation of the light emitters 3708and 3710 remotely.

As can be seen, the light source 3700 is configured (as described below)such that the light beams 3712 and 3714 leave the light source from thetransmission zone 3704 along substantially the same path. Mostpreferably they are co-linear. This arrangement provides the featurethat if the transmission zone 3704 is obstructed by a foreign body 3718as shown in FIG. 38 (again, for example, an insect crawling across thetransmission zone) the UV and IR light beams 3712 and 3714 areobstructed to a substantially equivalent degree.

When a foreign body 3718 obstructs the transmission zone 3704 it causessubstantially equal obstruction to both the first and second beams 3712and 3714, and the controller associated with the receiver will applyalarm and or fault logic to determine the cause of the decreasedreceived light level. The fault and alarm logic can be configured tointerpret an equivalent and simultaneous drop in received intensity inthe following manner. In some cases with a small drop in intensity thesystem may interpret this as a fault or obstruction. If the conditionpersists it can be compensated for in software or a fault conditionraised. With a large drop in intensity an alarm may be raised, eventhough the primary alarm criteria are based on differential attenuationof the two wavelength bands as described in our co-pending patentapplication.

FIGS. 37 and 38 provide one embodiment of a light source 3700 configuredto provide beams 3712 and 3714 that leave the light source 3726 from thetransmission zone 3704 along substantially co-linear paths. In thisembodiment light beams 3712 and 3714 do not originate from light sources3708 and 3710 that are physically proximate, but are brought intoproximity with each other prior to reaching the transmission zone withlight directing optics 3722. Light directing optics 3722 may be anyoptics suitable for directing light, such as mirrors, lenses (e.g.convex, concave, Fresnel lenses) and/or prisms, or a combinationthereof, and may also serve to collimate light beams 3712 and 3714.

FIG. 39 provides an alternative embodiment of a light emitter 3724configured such that the light beams 3712 and 3714 leave the lightsource from the transmission zone 3726 close together. In thisembodiment the first and second light emitters 3728 and 3730 aresemiconductor dies housed within a single optical package 3732 (thetransmission zone 3726 being the point at which the emitted light beams3712 and 3714 exit the package 3732). In this embodiment the proximityof light beams 3712 and 3714 is achieved by the physical proximity ofthe semiconductor dies 3728 and 3730 within the package 3732 and theleasing effect of the package 3732.

This may be achieved by using an LED with multiple semiconductor dies ina common LED package. Examples are depicted in FIGS. 47 to 49. As withtypical LED's, the housing is made of a clear material and shaped so asto have a lens effect on the emitted light beams that broadly constrainsthe beams to a forward direction.

In a further embodiment, and as shown in FIGS. 41 and 42, the lightsource 3700 is also provided with beam shaping optics 4102 for adjustingthe shape of light beams emitted from light emitters 3708 and 3710.Whilst depicted as a single element in FIG. 41, the beam shaping optics4102 may in practice (and as shown in FIG. 42) include a number of beamadjusting elements serving variously to adjust the beam width and/orbeam shape of light transmitted from the light source 3700 to thereceiver 3706.

Light beams 3712 and 3714 (from light emitters 3708 and 3710) passthrough the beam shaping optics 4202 which function to provide anadjusted beam 4104 with desired characteristics as discussed below.

As will be appreciated a beam will have a spatial intensity profile, orbeam profile, in a direction transverse to its axis. Using the beamprofile a beam width of a light beam can be defined between two pointsof equivalent intensity e.g. between the 3 db points either side of amaxima etc. One common measurement of beam width is the “full width athalf maximum” (FWHM) of the beam. For example, the adjusted beam 4204 inFIG. 42 is shown as having a wide section 4214 in which the intensity ofthe beam 4204 is above the predetermined threshold (depicted in black)fringed by lighter beam sections 4216 where the intensity of the beam isbelow the predetermined threshold.

The beam shaping optics 4102 can be chosen to achieve a desired beamprofile, and a collimating element 4208 serving to collimate light beams3712 and 3714 into a tighter beam shape. The collimating element 4208may, for example, be a lens such as a Fresnel lens or a convex lens, ormay be a reflector.

The beam adjusting optics can also include a diffusing element 4210,selected to “flatten” the beam profile and increase the beam width ofthe light beams 3712 and 3714. The diffusing element can be for examplea ground/etched/smoked glass diffuser. The diffusing element 4210 may,alternatively, be a coating applied to either the transmission zone 3704or another beam adjusting element.

FIG. 40 illustrates an exemplary optical element 4000 that shapes andflattens the beam profile. The optical element 4000 includes a Fresnellens 4080 placed back to back with a multi-element lens 4081. TheFresnel lens collimates the beam and the multi-element lens 4081effectively diffuses the beam. In place of the multi-element lens 4081another diffuser eg. ground, smoked or etched glass or surface could beused.

Providing a diffuser on the transmitter is advantageous as the receiverwill “see” an extended spot corresponding to the light source, ratherthan a point, which would be observed without the diffuser.Consequently, any foreign body (such as an insect) landing on thetransmission zone 3702 will cover a smaller proportion of thetransmission zone and therefore have a proportionally smaller effect onthe total light received at the receiver 3706. Moreover, in a multiplebeam system when all light emitters (3708 and 3710, i.e. light at boththe UV and IR wavelength) are diffused through a common element anyforeign body (such as an insect) landing on the transmission zone 3702will effect each wavelength of the light (i.e. UV and IR) bysubstantially the same amount.

Further by providing a greater beam width to the adjusted beam 4204alignment of the receiver 3706 with the light source 3700 is simplified.FIG. 43 provides a depiction of a receiver 4350 receiving a beam 4352from a light source 4354. By having a wide beam width the rate of changeof intensity across the beam width (near its centre) is reduced. Thismeans that as alignment of the beam and receiver drift over time, therate of change in received intensity near the centre of the beam, forsmall relative movements, is reduced compared to a beam with a narrowbeam width.

In this case the beam width 4356 of the beam 4352 corresponds to aboutthree sensor elements on the sensor 4350. If the system is configured toaverage (or aggregate) output these three pixels are used to determinethe received beam's strength, a small variation in alignment between thetransmitter and received will require either the system to accuratelytrack the beam movement on the sensor's surface or alternatively cause alarge variation in measured signal strength from the three pixels. Thisproblem's minimised using a wider beam width as shown in FIG. 44. Inthis system the beam 4462 emitted by the light surface 4454 has a width4456 equal to about the size of 6 sensor elements on sensor 4450. Aswill be appreciated such a system is more tolerant to alignment driftbefore the central 3 pixels lie outside the central high intensity beamregion.

The specific properties of the diffuser used and the beam width providedwill depend on the receiver and light emitters. Using LED's, however abeam width of approximately 10 degrees has been found to be a suitablecompromise between the preservation of intensity of the adjusted beamand width, so as to accommodate for easy alignment of the receiver withthe light source and drift of the receiver and/or light source.

Referring to FIG. 42, the profile adjusting element 4212 is selectedsuch that the beam profile of the adjusted beam 4204 extends further inthe horizontal direction than the vertical. This serves to maximise theintensity of the adjusted beam 4204 at the receiver whilst alsoaccommodating for the fact that building movement typically introducesmore variation in the horizontal plane than the vertical plane.

The light source can include a wavelength dependent profile adjustingelement 4212 for providing a different intensity profile to beams indifferent wavelength bands. The beam adjustment element may again be alens, reflector, coating or similar selected to provide the desired beamprofile at each wavelength is achieved.

The profile adjusting element 4212 has the effect of producing anadjusted beam 4204 having a beam profile in which the beam width of theUV light (originating from the UV emitter 3708) is wider than the beamwidth of IR light (originating from the IR emitter 3710). This isdepicted in FIGS. 45 and 46 where the light source 4500 transmits a beam4502 in which the beam width of the UV light 4504 is wider than the beamwidth of the IR light 4506. This has the advantage that in the eventthat the light source 4500 or receiver 4508 moves (e.g. due to buildingmovement) and the alignment therebetween is disrupted, the IR light 4506(having a narrower beam width) will move out of alignment with thereceiver 4508 (i.e. reducing the amount of IR light received at thereceiver) before the UV light 4504 does. This produces a decrease in IRlight intensity at the receiver, followed by a decrease in UV intensityas alignment become progressively worse. This is the opposite to theeffect seen when smoke enters the beam, when UV drops before IR. Hencethe misalignment can be distinguished from a smoke event by thefault/alarm logic of the controller.

As an alternative to using a profile adjusting element, a light sourcemay be used with a plurality of UV light emitters surrounding one ormore IR light emitters. In this case as the alignment of the lightsource and receiver is disrupted the receiver will cease to receive IRlight before it ceases to receive the UV light beam, thereby allowingthe receiver to interpret this as a fault rather than an alarm event.

In some embodiments an exotic intensity profile can be formed, e.g. anintensity profile having a sinc function or similar. In this case if asensor element or group of sensor elements of the receiver's sensordetects a variation in received beam intensity that matches the spatialintensity profile of the transmitted beam, it can be determined by thecontroller that the beam is sweeping across the sensor element or groupof sensor elements. This can be used by fault logic to detect and signalthat the system is drifting out of alignment and either re-alignment isneeded or soon will be needed.

FIG. 47 illustrates a light emitter 4740 which may be used in atransmitter of a beam detector according to an embodiment of the presentinvention. The light emitter 4740 includes a body 4742 in which ishoused one or more light emitting elements (not shown). The emitter 4740includes a lens or window portion 4744 through which the beams of lightgenerated by the light emitting elements are emitted. It also includes aplurality of leads 4746 for making electrical connection to the device.FIG. 47 illustrates a plan view of the same light emitter 4740. Thelight emitter 4740 includes a plurality of light emitting elements 4748,4750. In this case the light emitter is a LED and the light emittingelements are two LED dies in the form of a UV LED die 4748 and an IR LEDdie 4750 which constitute the light emitting elements. The package 4740also includes a photodiode 4752 within the body 4742. Each of the lightemitting elements 4748, 4750 are adapted to emit light through the lens4744. The photodiode 4752 receives some proportion of the light emittedby the light emitting elements 4748, 4750 and generates an electricalsignal which is fed to a feedback circuit. The photodiode output signalis used by the feedback circuit to adjust the output of the lightemitting elements to maintain correct operation of the light emitter4740.

FIG. 49 illustrates a second embodiment of a light source. In thisexample, the light emitter 4955 includes a plurality of light emittingelements arranged in a checkered pattern. In this case, the lightemitter 4955 includes four UV LED dies 4958 arranged around a central IRLED die 4960. As described above, this arrangement may have particularadvantages for preventing false alarms caused by a misalignment of thelight source with its respective receiver. The package 4955 alsoincludes a photo diode 4952.

FIG. 50 illustrates a schematic block diagram of circuit for atransmitter which may be used in an embodiment of the present invention.The circuit 5000 includes two light emitters 5002, 5004 which e.g.correspond to the infrared and UV LED dies as described above. It alsoincludes a photodiode 5006. As will be apparent from the abovedescription the LEDs and photodiode 5002, 5004, 5006 may be packagedclosely adjacent to each other within a single LED package. However,they may also be separately packaged in individual components. The lightemitters 5002, 5004 are electrically connected to a current source 5008and the photodiode 5006 is electrically connected to a feedback circuit5010. The feedback circuit 5010 is in communication with the currentsource 5008. In use, the output from the photodiode 5006 whichrepresents the output of LEDs 5002, 5004, is passed to the feedbackcircuit 5010 which in turn controls the output of the current source5008 to the light emitters 5002, 5004. As the received light signal atthe photodiode 5006 decreases, for example due to decreased light outputby the LEDs over time or through decreased light emission of the lightemitters 5002, 5004 due to an increase in temperature, the feedbackcircuit 5010 will apply an output to the current source 5008 whichcauses an increase in the drive current to the light sources 5002, 5004.In this way, the light output of the light emitters 5002, 5004 can bemaintained at an approximately constant level. Because the lightemitters may have different characteristics and predeterminedillumination characteristics required for correct system operation, theoutput of the two light emitters 5002, 5004 can be individuallycontrolled and adjusted. This can be achieved by alternatively pulsingtheir illumination and individually determining their light output usingthe photodiode 5006. Alternatively, multiple photodiodes could be usedin a manner in which their response is wavelength selective, and tunedto a corresponding light emitter. For example this may be achieved byproviding different bandpass filters over each of the photodiodes. Inthis case, the light emitters 5002, 5004 can be simultaneouslyilluminated and their outputs individually stabilised using a feedbackcircuit as described herein. FIG. 51 illustrates the feedback procedureof the circuit of FIG. 50 in stabilising the light output of one lightemitter which is continuously illuminated. The plot of FIG. 51 includesa first portion 5102 which represents the output of the photodiode overtime and represents a decrease in light output from the light sourceover time. This output is fed into the feedback circuit which controlsthe drive current output by the current source 5008. The decrease in thephotodiode output causes an increase in the LED output current as shownby plot 5104.

FIG. 52 illustrates a second circuit in a schematic block diagram form.In this example, rather than controlling the output current of thecurrent source, the duration of output pulses of the light emitters iscontrolled by the feedback circuit. Accordingly, FIG. 51 includes twolight sources 5202, 5204 each of which is connected to a current source5208. The circuit also includes a photodiode 5206 which is connected toa feedback circuit 5210. This circuit 5200 additionally includes a drivepulse modulation circuit 5212 which controls the timing and duration ofthe pulses of current applied to the light emitters 5202, 5204 by thecurrent source 5208. In this example, when a decrease in the receivedlight level received by the photodiode 5206 is sensed the feedbackcircuit 5210 applies a signal to the modulation circuit 5212. Inresponse, the modulation circuit 5212 increases the pulse lengthproduced by the current source 5208 that is applied to the LEDs.

FIG. 53 illustrates the method of operation of the circuit of FIG. 52.The top plot illustrates the output of the photodiode 5302, which as canbe seen, generally decreases over time. The lower plot 5304 illustratesthe drive current applied to the light emitters. In this case, theoutput current is applied in square wave pulses e.g. 5306. As the outputof the photodiode decreases the duration of the pulses increases overtime. By adjusting the pulse duration in this manner and maintaining thecurrent at a constant level the effective light intensity transmitted bythe light emitters, when integrated over the pulse length remainssubstantially constant. Advantageously it also results in more accuratereception of the pulses at the receiver since rather than the receiversimply taking a single sample of the light intensity within each pulsethe receiver can be operated as an integrator and collects more of thetransmitted signal.

The plots of FIGS. 51 and 53 illustrate the photodiode response anddrive circuit current for a single light emitting element of thetransmitter. A similar plot can be created for the other (or others)light emitting elements.

In another embodiment of the present invention open loop control of theLED intensity may be provided. For example, this may be achieved at lowcost by providing a current drive circuit that is temperature stabilisedor temperature compensated for the output characteristics of the LED.

In a further embodiment of the present invention the output of the lightemitting elements may only be weakly controlled, for example by beingdriven by a fixed pulse length with a very simple current controlcircuit. In this case, the averaged output intensity which is measuredby the photodiode can be communicated to the receiver. The receiver canthen be configured to compensate for the changing LED output insoftware. In a preferred form the averaged LED output can becommunicated to the receiver using an optical communications channel orother wireless communications channel. In a case where an opticalcommunications channel is used, this can be implemented by modulatingthe output of the light emitters themselves by inserting or omittingpulses in the sequence of illumination pulses of one or the other, orboth of the light emitters. This embodiment has the advantage ofrequiring only a relatively low cost transmitter without complexfeedback circuitry. It also takes advantage of the fact that temperatureand age related drift of the light emitter outputs is likely to berelatively slow so the bandwidth of the communications only needs to below.

A further problem that can arise in the methods described above whichuse one or more photodiodes to measure and control the output intensityof the light emitters is that ambient light may interfere with thismeasurement. For example, sunlight may be received by the photodiode anderroneously increase the detected output light level of the lightemitting element as detected by the photodiode.

To overcome this problem, in one embodiment, the effective ambient lightcan be greatly reduced by using a band pass filter in conjunction withthe photodiode. For example, a photodiode which only passes light in awavelength band emitted by its corresponding light emitter, but whichattenuates all other wavelengths e.g. those commonly occurring insunlight can be effectively used. Similarly, if artificial lighting suchas fluorescent lighting is used, the band pass filter can be adapted toexclude substantially all of the artificial light whilst stilltransmitting light in a wavelength band transmitted by the correspondinglight emitter.

In an alternative embodiment, light absorbing baffles may be positionedaround the photodiode e.g. in the LED package such that only light fromthe light emitting elements can reach the photodiode. The photodiode canbe shielded from external light by placing a baffle between thephotodiode and the lens of the LED package.

A further mechanism for correcting for background light levels is totake measurements from the photodiode when the light emitters are in‘on’ and ‘off’ conditions. In this case measurements taken during the‘off’ periods, between pulses of the light emitters, represent thebackground light. This background light level can be subtracted from thenext (or previous) light level measured during an ‘on’ period i.e. atime period in which a light emitter element is illuminated. Thebackground light level can be averaged over several ‘off’ frames and asliding average of the background level subtracted from the ‘on’ perioddata if smoothing of the background light levels is required. Forexample, this may be needed when the ambient light level varies greatlywith a frequency equal to or substantially equal to the pulse frequencyof the light emitters.

FIG. 54 illustrates a light source made in accordance with an embodimentof the present invention. The light source 5400 includes a light emitter5402 electrically connected to a control circuit 5404 which is poweredby a power source 5406. The light emitter 5402 projects a beam (orbeams) of light through an optical system 5408 towards a receiver. Insome embodiments, the optical system 5408 may simply be a transparentwindow through which the beam of light is projected in use, but also maybe a more complicated optical arrangement e.g. including one or morelenses, mirrors or filters etc. that are adapted to cause the beam oflight emitted by the light source 5402 to take on particular beamcharacteristics. As described above the external surface of the opticalcomponent 5408 is prone to temporary occlusion by insects or the like onits outer surface.

In order to detect these foreign bodies, the light source 5400 isprovided with a photodiode 5410 or other light sensitive element whichis connected to the control circuitry 5404. In use the photo diode 5410is arranged such that it will receive scattered light from foreignbodies occluding at least part of the outer surface of the opticalarrangement 5408. The photo diode 5410 is connected back to the controlcircuit 5404 which is adapted to determine based on the integrity of thereceived scattered light by photo diode 5410 whether a fault conditionexists. For example the control circuit 5404 can include a microcontroller 5412 which is programmed with, inter alia, fault logic whichcompares the received feedback signal from the photo diode 5410 to apredetermined threshold and if the received intensity is above thepredetermined threshold, or some other intensity and/or time basedcriteria are met by the feedback signal, the fault logic can be adaptedto trigger a fault response in the light source 5400. For example, themicrocontroller may cause an illumination pattern of the light emitter5402 to change in response to the fault condition to signal to areceiver of the particle detection system that a fault condition exists.By encoding a particular signal in the light emission patent the type offault could be signalled back to the receiver. The fault condition couldbe communicated by modulating the amplitude, duration and/or the timingof the transmitted light pulses in a predetermined fashion. This has theadvantage that no wiring or other wireless communication systems arerequired between the transmitter and receiver of the particle detectionsystem.

FIGS. 55 and 56 illustrate alternative embodiments of this aspect of thepresent invention, and common parts have been numbered with commonreference numerals.

Turning first to FIG. 55 which shows second embodiment of a light source5500 made in accordance with an embodiment of the present invention. Inthis embodiment, the light source 5500 has been provided with anadditional light emitting device 5502. This light emitting device isplaced such that it illuminates the lens from a shallow angle ofincidence. This increases the chance that particles or foreign bodieswhich fall on the external surface of the optical component 5408 willproduce a sufficient reflection to be detected by the photo diode 5410.In this embodiment, the photo diode can be shielded by a wall or baffle5504 to prevent direct illumination of it by the light source 5502.

FIG. 56 illustrates a light source 5600. This embodiment differs fromthe light sources illustrated in FIGS. 54 and 55 by the inclusion of anexternally mounted light emitter 5602. This light emitter 5602 ispositioned such that it illuminates the outside surface of the opticalcomponent 5408 directly. This may have additional advantages incorrectly identifying the presence of foreign bodies such as insects orthe like on the external surface.

In some embodiments of the present invention the light source may beprovided with an internally mounted feedback photo diode. This feedbackphoto diode is typically used to monitor the light output of the lightsource or sources and adjust the emission characteristics of the lightsource e.g. if a decrease in received light level is measured. However,the internal photo diode could be used with embodiments of this aspectof the invention by applying an upper threshold to its received signaland if the received light level is above the upper threshold (and is notthe result of an increase in light output caused by the controller 5404)this may be determined to be the result of a foreign body on theexternal surface of the optical system 5408.

An embodiment of the present invention may also be able to be used witha receiver of a particle detection system. In this embodiment, thereceiver can be fitted with a light emitter such as that in FIG. 14 andphoto diode and be configured to implement the method as describedherein in relation to a light source. With the receiver, it is clearlyadvantageous that the transmission of light within the receiver housingdoes not interfere with the particle detection performance of thesystem. Accordingly, the light source 5502 can be selected such that itemits light outside the reception band of the receiver, or the receivercan be provided with a band pass filter which excludes the selectedwavelength. Alternatively, if the light source of the particle detectoris set to flash according to a predetermined pattern with ‘off periods’between flashes the foreign body detection function can be performed inthese ‘off’ periods. If foreign body detection in the ‘off’ periods isto be used the light emitter e.g. emitter 5502, can emit light in thepass band of the receiver and the main receiver could be used to detectthe presence of foreign bodies on the external surface of the opticalcomponent 5408.

As noted above, it is important for particle detectors to be properlyinstalled and commissioned. Correct installation and commissioningensures reliable and safe operation of the system. In this regardseveral processes that can be used in the set-up and commissioning of aparticle detection system will now be described.

For the purposes of clarity, the following process description willfocus on a particle detector as described in relation to FIG. 2.However, the process may be implemented using the implementationsdescribed in relation to FIG. 3 and other implementations, which will beapparent to a person skilled in the relevant art.

In one embodiment, the process includes two stages, comprising acommissioning stage and an operation stage. The commissioning stage isperformed on initial installation of the beam detector, whereas theoperation stage is performed some time after installation.

A process for commissioning the particle detector is shown in FIG. 58. Atechnician or other suitable installer mounts the light source 32, andreceiver 34 and target 36 (which is optional in other geometries) inappropriate locations spanning an area requiring monitoring forparticles e.g. smoke (step 5801). As discussed, with the use of areceiver 34 in the form of a video camera or other suitable device, theprocess of installation may be easier and quicker.

Following installation, in step 5802, the technician activates thedetector by powering the particle detector. Initially the detectordiscovers the presence of light sources within its field of view tomonitor. As described elsewhere here and in our co-pending applicationthe controller identifies the relevant portion(s) of the detector'sfield of view that represent light from the light source 32 and thenmeasures the strength of the light signal received from the light source32, in step 5803. This identification process may be manual, for examplewith the technician interfacing a portable computer to the receiver 34,viewing the image captured by the camera and indicating using a pointand click device or otherwise the relevant portions of the field ofview. The identification process may instead be automatic, for examplewith the controller 44 programmed to identify the parts of the screenilluminated by the light source (e.g. UV and/or infrared light in thecase that UV and/or ultraviolet light sources are used).

A detailed description of an exemplary method of target acquisition andtiming discovery can be found elsewhere herein.

The level of light received from each identified source is compared to athreshold value to determine if the received light level is withinacceptable limits in step 5804. If the controller 54 receives light fromthe light source 32 above a preset threshold, then it causes theparticle detector to indicate acceptable operation (step 5805).Indication of the status of the system can comprise constantly lightingan LED on the receiver 34, although other notification mechanisms may beused such as making a sound and/or transmitting a signal to a PDA orcomputer in communication with the controller 44, for viewing by thetechnician.

The detection system will apply alarm and fault logic to determineeither whether the detection system is operating correctly or whetherparticles have been detected. The alarm and fault logic will includealarm criteria based on the intensity of light received at the receiver.This criteria may be based on raw intensity measurements, differentialor comparative values at multiple wavelengths or rates of change orother measures known to those skilled in the art. Typically the criteriacan be seen as a comparison of received data to a threshold level. Theinventors have realised that since Installation and commissioning of theparticle detection system is supervised by the technician and duringcommissioning the system is not relied on to provide a particledetection or life safety function, the usual alarm thresholds may belargely ignored in the commissioning stage. Thus the thresholds appliedduring commissioning stage can be set very tightly in comparison to oneor more of the alarm or fault thresholds that are applied during theoperating stage.

In a preferred form at least one threshold used in the commissioningstage will be set substantially above a level that would cause theparticle detector to generate an alarm, take other action indicatingthat smoke has been detected or raise a or fault in the operation phase.

For example the acceptable minimum level of light received during thecommissioning stage could be set 20% over a light level that would causea fault condition during normal operation. Such a threshold requires aninstaller to ensure that the initial alignment of the system is highlyaccurate, the optical surfaces are clean and in good condition and thatthe transmission path length is not outside acceptable ranges, otherwisethe system would not achieve the relatively stringent light intensityrequirements in place during commissioning.

If during the commissioning stage the controller 44 determines that theintensity of the light received is below the preset threshold, then thecontroller 44 causes the particle detector to indicate an error (step5806). This may, for example, comprise flashing an LED or transmitting asignal to a PDA or computer of the technician. If the identification ofthe relevant portions of the field of view is automatic, the controller44 may allow a manual identification process to be completed, followingwhich steps 5802 to 5804 may be repeated.

On receipt of the error indication, the technician can perform thenecessary action to rectify the problem. For example the technician canreposition the light source 32, receiver 34 and/or target 36, forexample to reduce the path length between the light source 32 and thereceiver 34. Where a substantial reduction in path length is requiredand the initial installation used the target 36, the technician mayremove the target 36 and place the receiver 34 where the target 36 waspreviously located, to halve the path length. The technician couldotherwise locate a suitable mid-point on which to mount the componentsof the particle detector.

The controller 44 may be programmed to complete its part of the processshown in FIG. 58 automatically on each power up. Alternatively, theprocess may be completed only on command, for example by the pressing ofa button associated with the receiver 34, or on receipt of a commandthrough a communication port of the receiver 34.

If the commissioning stage has been successfully completed, the receiver34 is in condition to start operating. Two embodiments of this‘operation stage’ are described below, the first in relation to FIG. 59and the second in relation to FIG. 60. During the operation stage, thereceiver 34 measures the intensity of light received from the lightsource(s) 32. This data is processed, and if the signal(s) receivedindicates smoke is present in the light path between the light source(s)32 and the receiver 34, the controller 44 generates an alarm conditionin the particle detector, and/or communicates a signal to cause anotherdevice (e.g. a fire panel) or system such as an automated evacuationsystem, to generate an alarm.

In the preferred embodiments of the present invention, which operate amultiple wavelengths, the primary alarm thresholds are based on adifferential measure of received light intensity at more than onewavelength, e.g. the ratio or difference between received lightintensity at two wavelength, or rates of change of such measures. Asecondary “fallback” threshold can be set on the basis of the absoluteor corrected received light intensity at one or more wavelengthsindependently. The detection of correct operation and fault conditionscan also be based on both differential or absolute received light level.

Referring to FIG. 59, the controller 44 is programmed to re-check thesignal strength received from the light source 32, or each light source32 (if there is more than one) against an absolute signal strengththreshold. This check may be performed continuously or periodically, forexample, once a day, two or more times a day, or at a lesser frequency,depending on requirements. The check may also be performed on command,for example on receipt of a command to check the signal strengthreceived at a communication port of the receiver 34, or on actuation ofa button provided in association with the receiver 34. If the controller44 determines in step 5907 that no check is required, the receiver 34continues to monitor for smoke in the light path.

If a check is required, then in step 5908 the controller 44 evaluatesthe signal strength of the light from the light source(s) 32 and in step5909 compares this to a threshold value. This threshold value may be thesame as that used in step 5803, or may alternatively be another setvalue, determined to indicate a required level of reliability ofoperation.

In step 5910, the result of the comparison is evaluated and if thethreshold value for minimum required intensity has not been exceeded, anerror is indicated/generated (step 5911), which error may be the same asor different to the error indicated in step 5806, depending on theparticular implementation. For example, the error indicated in step 5911may be an audible signal generated at the site of the particle detector,and/or at a control station, such as a security station for a building,and/or a remote monitoring station by communicating the error over awired and/or wireless public and/or proprietary network.

If the threshold value for minimum required intensity has been exceeded,then in step 5912, the particle detector indicates acceptable operation,which may be indicated in the same was as described for step 5805.

Referring to FIG. 60, a flow chart of a process that may be completed bythe controller 44 to implement an alternative operation stage is shown.

Following commissioning (i.e. following step 5805), the controller 44 instep 6016 determines if a delay period has expired. This delay periodmay, for example, be 24 hours, after which time it would be expectedthat the particle detector is operating in a stable condition. Othernon-zero delay periods may be used in other embodiments. Preferablyduring the delay period the detector is not used for essential particledetection purposes, and is only being monitored for correct operation.

When the delay period has expired, the controller 44 re-sets itsthresholds (in step 6018). Preferably the new thresholds to be used arebased on either the measured signal strength (or parameter derivedtherefrom) that was measured in (optional step) 6015. Alternatively, itcould be based on a measurement(s) made upon the expiry of the delay(step 6017). The operational threshold intensity could also have apreset minimum value. Alternatively an acceptable threshold can bedetermined by looking at the performance of the system during the delayperiod, e.g. by analysing the variation of received light intensity atone or more wavelengths during the delay period. For example if thevariation in received light intensity over the period caused by thingsother than the impingement of particles of interest into the beam (e.g.mounting drift, temperature dependent light output variations of thelight sources etc.) is 2% then an acceptable minimum received lightlevel could be set at 2% below the average received light level, or atsome other level. The operational intensity may be a function of boththe measured intensity at the end of the delay period and a presetminimum value, for example determined as the average of the two values.The operational threshold and present minimum value, if any, may bedetermined/set independently for each light path if there is more thanone light path.

Next the controller evaluates the intensity of the light received fromthe light source(s) 32 (step 6088A) and compares it to the newoperational threshold in step 609A.

Steps 600A to 602A may then proceed as described herein above inrelation to FIG. 59, using the operational threshold value determined instep 689A.

Where there are multiple light sources and/or multiple light paths froma single light source, the error may be indicated when the intensity oflight received along any one of the monitored light paths falls belowthe threshold. Alternatively, there may be different levels of errorcondition, with one level indicating when light along one of the lightpaths falls below the threshold and another level indicating when lightalone more than one or all paths falls below the threshold. Thethreshold may be different for each light path, reflecting for exampledifferences in the intensity of light generated by the light source 32for that path.

In the foregoing description, reference has been made to individuallight paths from the light source(s) 32 to the receiver 34. Thoseskilled in the relevant art will appreciate that light may be reflectedoff various structures, such as a ceiling, and as a result there may bemore than one light path between a light source and a particular pointon a receiver. Implementations where light from a source is received bythe receiver by multiple paths and where light from one light source isreflected onto the part of the receiver receiving light from anotherlight source are intended to be within the scope of the presentinvention.

Turning again to FIG. 57, in an installation such as this, thedifference in the intensity of light arriving at the receiver 5702 fromthe transmitters 5704, 5706, 5708 can be adjusted in an embodiment of afurther aspect of the invention by applying an optical attenuator to theoptical path of each transmitter in the system, or at least thosetransmitters in the system which are located at a distance likely tocause saturation of the receiver 5702. FIG. 61 shows exemplary housingwhich may be used to implement this mechanism. FIG. 61 shows a crosssectional view through a transmitter housing 6100. Within the housingthere is located a light source such as an LED 6102. This is connectedto appropriate circuitry (not shown) and is used to generate a beam oflight for use in particle detection. The light emitted by the lightsource 6102 may pass through one or more optical elements 6104 forfocusing the beam into an appropriate shape eg a narrowly divergingcolumn or broad divergent beam, or some other shape as discussed herein.The transmitter 6100 additional includes one or more optical attenuators6108 for attenuating the beam emitted from the transmitter 6100. Thelevel of attenuation can be selected and set at an appropriate level forthe separation between the transmitter and its corresponding receiver byusing one or more filters 6108 having suitable ???? characteristics.Multiple filtering elements can be added in series to achieve theappropriate attenuation level. An example of a system with multiplefilters is shown in FIG. 62. In FIG. 62 like components have beennumbered to correspond to FIG. 61. In a preferred embodiment the housing6106 of the transmitter 6100 can be configured to have structures 6112for receiving the filters 6108 (and 6110) in the appropriate position.Most preferably, the receiving mechanism enables selectable filters tobe attached and removed by the installer during commissioning of thesystem. For example, the housing can include a plurality of grooves,e.g. grooves 6112, which are each adapted to receive an individualfilter element.

FIG. 63 shows three exemplary filter elements which may be used with anembodiment of the present invention such as that illustrated in FIG. 61or 62. The filters 6300, 6301, 6302 are preferably neutral densityfilters and can be made of an attenuating material, such as a plasticfilm. Attenuators for different distances can be made by increasing thelevel of absorption of the material e.g. by changing material propertiesor increasing thickness of the material.

Preferably each filter has indicia indicating the strength of thefilter. For example, an indication of a preferred distance or distancerange between the transmitter and receiver can be printed, embossed orotherwise displayed on the filter. Alternatively, a fractionalattenuation level can be displayed. This information displayed on thefilters can be used by the installers to determine the appropriatefilter or group of filters to use with a transmitter for the particularsystem geometry being installed.

An alternative (or complimentary) embodiment of this aspect of theinvention will now be described. In this embodiment the system isadapted to enable the receiver to avoid saturation without the use of afilter, although filters could be used with this embodiment ifnecessary. FIG. 64 is a timing diagram illustrating a second solution tothe abovementioned problem according to an aspect of the presentinvention.

In this aspect of the invention a transmitter can be configured to emita sequence of pulses of differing intensity and to repeat this sequenceduring operation. The receiver can then determine which of the receivedpulses falls within an acceptable light level at the receiver and fromthat time forward choose to receive only those pulses which have anacceptable light level.

Turning now to FIG. 64 the uppermost plot 6400 is a timing diagramshowing the transmission power of a sequence of pulses emitted by atransmitter over time. The lower plot shows the reception state of thereceiver. In an initial time period t₁ the transmitter cycles through asequence of transmission pulses 6404, 6406 and 6408 of progressivelyincreasing transmission power. This sequence is repeated in time periodst₂ and t₃ and continuously thereafter. In the first time period t₁ thereceiver does not know which transmission pulse is going to be at theappropriate level so as not to saturate the receiver but also be highenough to have adequate signal to noise ratio. Therefore, for timeperiod t₁ the receiver is continuously in an “on” state and is able toreceive each of the transmitted pulses 6404, 6406 and 6408. On the basisof measured intensity of the three received pulses the receiver candetermine which pulse should be received from then on. In this case, thepulse 6408 is determined to have the correct intensity and the receiveris configured to be activated at times 6410 and 6412 which correspond tothe time of transmission of pulse 6408 in the successive transmissionperiods T2 and T3.

As described above the receiver and transmitter are generally not incommunication with each other, and the transmitter will continue to emitthree different level pulses throughout its operation. Alternatively, inan embodiment where the receiver may communicate back to thetransmitter, the receiver can signal to the transmitter which of thepulses to continue emitting and which of the pulses to omit. Such asystem will reduce the power consumption of the transmitter as fewerpulses will be emitted.

The initial period of monitoring the various transmission pulses may beextended beyond the single transmission time period as it may benecessary for the receiver to discover the pattern of illumination ofthe transmitter over several transmission time periods.

In a third solution for ameliorating or addressing this problem afurther aspect of the present invention uses electronic means to controlthe transmission power of the transmitter. In this example a DIP switchcan be incorporated into the transmitter which during installation isset to the appropriate transmission level by the installer. The settingon the DIP switch can be chosen to either reduce the current through theLED and thus dim the LED or reduce the duration of the pulse “on period”to avoid saturation of the receiver. In this case it may be advantageousto have an installation mode in which the transmitter emits light atdiffering power levels initially. During this period the receiver candetermine the appropriate transmission level and indicate to theinstaller the appropriate DIP switch setting (or settings) to be made toset the transmission level to the most preferable value. For example,the receiver may be provided with a display or other interface that canbe used to indicate the DIP switch settings for the transmitter. Itshould also be appreciated that in a system with a plurality oftransmitters any process can be repeated for each transmitter.

In a further embodiment of this aspect of the present invention a systemhaving multiple transmitters may include transmitters of different typesin it. Each transmitter type can be optimised for use at a particulardistance or range of distances and in this case is up to the installerto select what type of transmitter should be installed.

FIG. 65 illustrates an embodiment of a particle detection system 6500being tested using a test filter according to an embodiment of anotheraspect of the present invention. The particle detection system 6500includes a light source 6502 a light receiver 6504. The light source6502 generates one or more beams of light including light in a firstwavelength band 6506 which is in a wavelength band centred at λ1 and asecond wavelength band 6508 centred at λ2. Preferably, λ1 is a shorterwavelength band, for example in the ultraviolet part of theelectromagnetic spectrum, and λ2 is a longer wavelength band e.g.centred in the near infrared. The light beams 6506 and 6508 pass througha test filter 6510 which mimics the effect of smoke on the beam byalternating the beams 6506, 6508. The operation of the receiver 6504 canthen be checked to determine if its behaviour is correct given theextent of beam attenuation being caused by test filter 6510. Because thelight emitted by light source 6502 includes light in two wavelengthbands λ1 and λ2 the filter 6510 needs absorption characteristics whichtreat these two wavelength bands in an appropriate manner. In apreferred form of particle detector 6500, as described above, adifferential measure of light intensity in the two wavelength bands λ1and λ2 (e.g. ratio of measured intensities at each wavelength or a rateof change of these values etc.) is used to determine the presence ofparticles of a predetermined size range within the beams 6506 and 6508.Most preferably, if the ratio of the received light intensities variesin a predetermined manner then a particle detection event may beindicated. Accordingly, in most cases the test filter 6510 does notattenuate both wavelength bands evenly but must provide a differentialattenuation in the two wavelength bands λ1 and λ2 to mimic the effect ofsmoke. In this example, the test filter 6510 absorbs the shorterwavelength λ1 significantly more than the longer wavelength λ2. Forexample, the test filter can absorb twice as much of the light in λ1 asit does in λ2, which may be determined to look like a particular type ofparticle.

Thus the test filter characteristics are chosen to set both the ratio oflight transmitted (or attenuated) in different wavelength bands and toalso to vary the absolute level of light transmitted (attenuated) by thetest filter. These two variables can be adapted to produce a suitabletest filter to mimic different smoke or particle types as well asdifferent smoke or particle densities.

FIG. 66 illustrates a first exemplary test filter comprising threefilter elements 6512, 6514 and 6516. The test filter 6510 is a generallysheet like material formed by three layers of filter material. In thisexample, the first two filter elements 6512 and 6514 attenuate light inwavelength band λ1 and the third filter element 6516 absorbs light inwavelength band λ2. In this example each of the filter elements 6512 to6516 making up the test filter 6510 are configured to provide the sameamount of attenuation of light passing through it. Accordingly, the testfilter 6510 attenuates light in wavelength band λ1 twice as strongly asit does light in wavelength band λ2.

FIG. 67 illustrates a transmission spectrum for the test filter 6570. Ascan be seen, the test filter transmits substantially all of the lightoutside wavelength bands λ1 and λ2 but attenuates about twice as much ofthe light in wavelength band λ1 as it does light in wavelength band λ2.In other embodiments transmission outside wavelength bands λ1 and λ2 canbe any level and need not be uniform over all wavelengths.

The absorption characteristics described above can be achieved in a widevariety of ways. FIGS. 68 to 75 illustrate a range of these techniques.Others may be apparent to those skilled in the art.

FIG. 68 illustrates a filter element. The filter element has a frontface 6802 to which is adhered a plurality of particles having a particlesize distribution substantially equal to the particles to be detectedusing the particle detector to be tested using the filter element. Suchparticles can be manufactured using a number of well known processes orselected by filtration and separation from powder such as aluminiumoxide. FIG. 69B illustrates a variant on this mechanism. The filterelement 6900 of FIG. 15B includes particles similar to those used in theembodiment of FIG. 68, but distributed through the bulk of the filterelement.

FIG. 70 shows a filter element 7000 on which one or both surfaces hashad a surface treatment to cause defects on the surface of the material.Surface defects can be generated for example by mechanical abrasion,particle blasting, chemical or laser etching or the like. Alternativelydefects may be created through the bulk of the filter element in FIG. 70using for example 3D laser etching.

FIGS. 71 and 72 illustrate further surface treatments that can beperformed on filter element 7100, 7200 to achieve predeterminedattenuation characteristics. In these examples the filter element isformed of a substantially transparent material and is modified by theapplication of surface printing. For example, an inkjet or laser printercan be used to print a pattern on one or both surfaces of the filterelement sheet. Preferably, a pattern of dots is printed over the entiresurface of the filter element. Most preferably the dots of a uniformsize are printed at a predetermined separation which is determined bythe level of attenuation to be achieved by the filter element. FIGS. 71and 72 are substantially identical apart from the number of dots printedon the filter element. As can be seen, FIG. 71 has far less dots printedon it than FIG. 72 and accordingly will be less absorptive than thefilter element of FIG. 15E.

Obviously other patterns can be used to achieve a predeterminedattenuation.

FIG. 73 illustrates a printing pattern which can be implemented on asurface of a filter element 7300. This filter element 7300 is printedwith two colour printing process and includes a dot pattern which hasdots of a first colour 7304 and dots of a second colour 7306. As can beseen there are more dots of colour 6804 than of colour 6806 andaccordingly the filter element will attenuate more light in onewavelength band than the other. Alternatively, a dot pattern in onecolour, could be printed on one side of the filter element and a dotpattern on the other side can be printed in the second colour.

FIG. 74 illustrates a test filter having a more complex structure. Thistest filter element 7408 is made of five layers 7410 to 7418. Four ofthe layers 7410 to 7416 attenuate light in wavelength band λ1 but aretransmissive to all other wavelength bands, and the last layer 6818absorbs at wavelength band λ2.

FIG. 75 illustrates another test filter. This test filter has a centralportion 7420 which has characteristics chosen to achieve a predeterminedattenuation of light in wavelength bands λ1 and λ2 but it is laminatedwith transparent layer 7422 and 7424 to protect the attenuating layersforming the core 7420. This can be particularly advantageous where theattenuating layers use a surface treatment which may be damaged bycontact with other objects or substances.

In another embodiment one or both of the surfaces of the test filter canbe treated with a plurality of thin films to create a predeterminedwavelength selective attenuation profile. Moreover, the filter elementscan be reflective rather than absorptive, to achieve the desiredattenuation profile.

FIG. 76 illustrates a beam detector 7600 which includes a transmitter orlight source 7602 and receiver 7604. The transmitter 7602 includes oneor more light emitters 7606 which are adapted to generate one or morebeams of light 7608. At least a portion of the one or more beams arereceived by the receiver 7604. Preferably, the light emitter 7606 isadapted to simultaneously generate light within two wavelength bandscentered at different wavelengths λ₁ and λ₂ hereinafter termed“wavelength bands λ₁ and λ₂” for transmission to the receiver 7604. Thereceiver 7604 includes a light sensor 7610 which is adapted to output asignal representing the received light intensity at a plurality ofpositions on its surface in the two wavelength bands. The output in thetwo wavelength bands is passed to a controller 7612 which performsanalysis on the output of the light receiver 7604 and applies alarmand/or fault logic to determine whether an action needs to be performedin response to the received signal or signals. The receiver 7604 mayadditionally include optical system 7614 for forming an image orotherwise controlling the received beam 7608.

In an embodiment of the present invention where the light emitter 7606simultaneously emits in two wavelength bands λ₁ and λ₂ the sensor 7610of the receiver 7604 is preferably adapted to simultaneously anddistinguishably receive light in each of the wavelength bands. In orderto achieve this aim, the receiver 7604 can be provided with wavelengthselective component which is adapted to split light in wavelength bandλ₁ from light and wavelength band λ₂ and differentially direct them tothe sensor 7610 in a manner which enables the two wavelength componentsto be separately measured.

FIG. 77 illustrates a first example of a receiver 7750 which enablesthis technique to be performed. The receiver 7750 includes a window 7752through which a light beam 7754 enters the receiver 7750. The window7752 may be a flat piece of glass or similar or alternatively may bepart of an optical arrangement (e.g. a lens or series of lenses) adaptedto form an image on or near the light receiver. The receiver 7750includes a sensor 7756 which includes a plurality of sensor elements7758. A wavelength selective component 7760 is mounted adjacent thefront face of the light sensor 7756 and comprises for example, a mosaicdye filter. The dye filter 7760 includes a plurality of cells 7762 and7764. The cells 7762 are adapted to be transmissive in a firstwavelength band λ₁ and the cells 7764 are adapted to be transmissive ina second wavelength band λ₂. The combination of mosaic dye filter 7760and light sensor array 7756 enables a first group of sensor elements orpixels of the sensor 7756 to receive light in the first wavelength bandwhilst other pixels of the sensor array 7756 simultaneously receive andrecord light intensity use in a second wavelength band λ₂.

The controller can then be configured to separate the intensity valuesin one group (i.e. relating to one wavelength band) from the other, e.g.the outputs of the sensor elements can be selectively “read out” toobtain the two wavelength band signals.

FIG. 78 shows an alternative embodiment which achieves a similar result.In this embodiment the receiver 7800 is similar to that of FIG. 77 inthat it includes an optical component 7802 which may comprise a windowor focusing optics through which light enters the receiver housing 7804.After passing through the optical component 7802 the beam enters awavelength selective prism 7806 which is adapted to divert light indifferent directions depending upon the wavelength of the incidentlight. Accordingly, light in wavelength band λ₁ is transmitted into afirst beam 7808 whereas light in wavelength band λ₂ is transmitted in asecond beam 7810. The beam in wavelength band λ₁ falls on a first sensorarray 7812 and light in the second wavelength band λ₂ falls on a secondsensor array 7814. As previously described in relation to earlierembodiments, the sensor arrays 7812 and 7814 are adapted to record theintensity of light at a plurality of points on its surfacesimultaneously.

FIG. 79 shows a second embodiment using a prism to split a beam into itswavelength components. In this embodiment the receiver 7820 includes asingle sensor array 7822 adapted to receive light via an opticalcomponent 7824 and a beam splitting component 7826. The beam splittingcomponent is adapted to split light in a first wavelength band fromlight in a second wavelength band and to direct these in differentdirections. This embodiment differs to that of FIG. 78 in that ratherthan forming images in each of the wavelength bands λ₁ and λ₂ onseparate sensor arrays the beam splitting component 7826 is mounted veryclose to the sensor array 7822. In this way, as the beam splitting takesplace very close to the surface of the sensor array 7822. Effectively,this provides a separate wavelength selective beam splitter for a subsetof pixels of the sensor element 7822.

FIG. 80 illustrates a further embodiment of the present invention. Thisembodiment illustrates a light receiver 7850 including a housing 7852 inwhich is mounted a sensor element 7854. Light enters the housing throughan optical system 7856 and is transmitted to the light sensor 7854. Inthis embodiment, the sensor 7854 is a multi-layered sensor and includesn sensor layers 7854.1, 7854.2 through 7854.n. Each sensor layer 7854.1through 7854.n is adapted to receive light at a different energy. Thisenergy separation is achieved by taking advantage of the phenomenon thatdifferent energy photons will penetrate at different depths into thesensor device 7854. In this case the sensor device can be a siliconlight sensing element. In each layer of the sensor 7854 a spatiallydistinct measure of light intensity can be determined at itscorresponding wavelength.

In each of the embodiments described above the signals at a plurality ofwavelengths can be processed in accordance with the aforementionedmethods to produce a particle detection or fault condition output.

It should be appreciated that although the preferred embodiments weredescribed in connection with the two wavelength system, three or morewavelengths may be used in some embodiments.

FIGS. 81 and 82 show one embodiment of the present invention thatincludes a transmitter 8101 for emitting at least one beam of light8102, and a receiver 8103 for receiving the beam. The receiver 8103 hasa light sensor having multiple photosensitive elements 8104. An exampleof a suitable receiver is a video imager whose sensors are arranged intoa matrix of pixels. Each sensor element produces an electric signal thatis related e.g. proportionally, to the intensity of the light detectedby that sensor.

In FIG. 81, the transmitter 8101 is shown as being positioned oppositethe receiver 8103 across a monitored space 8105. However it should beunderstood that the transmitter 8101 can be otherwise located (i.e. notdirectly aiming the emitted beam toward the receiver 8103) as long asthe emitted beam 8102 crosses the monitored space 8105. The emitted beam8102 can be directed toward the receiver 8103 by an arrangement such asan optical reflector.

A diffusing means 8106 is provided in the path of the emitted beam 8102,so as to produce a deliberately diffused image of the beam on thereceiver's sensor 8107A. Signals from the sensor elements 8104 aretransmitted to a controller 8108, such as a processor.

The controller 8108 combines the signals from at least some of thesensor elements e.g. only those on which the beam falls, group 8109 todetermine the intensity of the received beam 8107A. Each sensor elementin the CCD 8103 can have a different inherent noise level, and adifferent light conversion efficiency. Therefore, in its calculations,the controller 8108 takes into account information regarding the sensorelements 8109A that are initially in alignment with the beam 8107A.Based on the determined intensity, the controller 8108 applies alarmlogic and decides whether any action, such as signalling an alarm, ordispatching an alert or a message to an administrator or another user,should be taken. In previously described systems, the decision has beenmade based on whether the determined intensity is lower than a thresholdvalue that corresponds to a presence of smoke particles.

In FIG. 82, the position of the transmitter 8101 is shown as beingslightly removed from its position as shown in FIG. 81. This changeresults in a change in the position of the diffused beam image 8107B,relative to the receiver 8103. Some of the sensor elements onto whichthe diffused beam 8107B is incident are outside the initial subgroup ofsensor elements 8109 whose signals are initially read by the controller8108. The controller 8108 is adapted to track the position of the imageof the beam across the surface of the sensor 8103 and consequentlyintegrates the received light over sensors in a new region 8109A. Aswould be appreciated the group of sensors within the region 8109A isdifferent to that which was originally used as group 8109, but the twogroups (8109, 8109A) include the same number of sensors.

The sensor elements in the new region 8109A theoretically can have adifferent inherent signal error than the sensor elements in the originalregion 8109. However, this difference is not significant. In thisexample the average inherent noise level of the four newly integratedsensor elements will be about the same as that of the four sensorelements that are no longer used. Moreover, the spacing (i.e. number andsize of gaps) between sensor elements remains substantially constant andthus no additional light is lost in the gaps between sensors elements.

This can be contrasted to the case of a sharply focused beam image wherethe error related to the received beam strength will change dramaticallyas the sharply focused beam moves from one sensor element to the nextbecause the two sensors have different light conversion efficiencies andthe difference is not ameliorated by averaging (as in the case of a morediffused beam image). Further, as the focused beam moves from one sensorelement to the next it will scan past the space between the sensorelements, and there will be an intervening period where a substantialamount of the beam power will be lost in the space between the sensors.As described above, these problems are mitigated by use of a defocusedimage.

The following paragraphs describe examples of how the optics (i.e.imaging system) used in the receiver can be arranged so as to produce adeliberately defocused target. In this specification, the term‘diffusing means’ should be read broadly to refer to any arrangement orcomponent that produces a diffused image of the beam on the sensor.

In the embodiment illustrated in FIG. 83, the diffusing means 8301includes a focusing lens 8302 that is located in the emitted beam'spath.

The focusing lens 8302 has an associated focal point 8304. The emittedbeam 8303 is either transmitted directly by the transmitter (not shown)toward the lens 8302 or toward a reflector (not shown) that reflects thebeam toward the lens 8302. In this embodiment, the relative positions ofthe lens 8302 and the sensor 8305 are such that the sensor is displacedfrom the position where the focused beam image 8306 is located. Thesensors 8305 therefore receive a beam image that is deliberatelyslightly defocused. The amount of focus and the amount of diffusion arecontrolled so that the signal to noise ratio can be obtained (achievedwith a more tightly focused beam) while achieving a system that isrelatively stable (achieved with a diffused or blurred image) even whenthere are movements in the system.

In a further embodiment (FIG. 84), the receiver 8310 includes a focusinglens 8311. The light sensor 8312 is placed at the spot where the focusedimage is located. The diffusing means in this embodiment includes adiffuser 8313 that is placed somewhere between the lens 8311 and thelight sensor 8312 (e.g. directly over the sensors). The received imageis therefore deliberately blurred. The diffuser 8313 can be a piece ofground or etched glass or simply comprise an etched face on the sensoritself.

In some cases, the diffusing means 8313 can be located somewhere in theemitted beam's path to the sensor 8312.

In some embodiments the transmitter may output a light beam havingcomponents in two (or more) wavelength bands, for example infrared (IR)and ultraviolet (UV) light bands, both emitted along a substantiallycollinear path. The two wavelengths are chosen such that they displaydifferent behaviour in the presence of particles to be detected, e.g.smoke particles. In this way the relative change in the received lightat the two (or more) wavelengths can be used to give an indication ofwhat has caused attenuation of the beam.

In some embodiments, the receiver may receive multiple beams, ormultiple transmitters may emit beams to be received. The multiple beamsare used together for the purpose of smoke detection in the monitoredspace. As with the previous embodiments, the sensors receive the beamsand send signals to the controller. The controller analyses the signals,and determines which portion of the signals contains information moststrongly related to the respective beams. At the conclusion of thisdecision process, the controller will have selected two portions ofsignals that are produced by respective individual sensors or groups ofsensors, so the selected signal can most reliably be used to measure theintensity of beams. One way of selecting the sensors whose data can bemost reliably used is to view the image generated by the receiver at thetime of commissioning the smoke detector and selecting the appropriatesensors.

A further mechanism of ensuring that the calculated received beamintensity is as close to the actual intensity of the received beam aspossible, may be performed by the controller. The controller may decidewhether to use the value corresponding to a certain sensor element,according to that element's contribution to the overall image strength.For example, from the sensor element outputs, the controller candetermine a ‘centre-of-signal’ position of the beam. Thecentre-of-signal position is analogous to the centre of mass position,except that instead of mass, it is the signal value contributed by eachpixel (i.e. sensor element) that is used in the calculation. Forexample, the following equation may be used:Centre-of-signal position vector={sum of (position vector of eachpixel)*(value of each pixel)}/{sum of values from all the pixels}.

After the centre-of-signal position is determined, the controller mayweight the signal contributed to the received beam intensity value byeach sensor element (i.e. corresponding to the electrical signalgenerated by each sensor) according to the distance between that sensorelement and the centre-of-signal position. In this way, the controllerdetermines the sensor elements whose signals best represent the targetimage and that are least likely to be dropped from subsequentmeasurements due to drift in the beam image's position on the sensor.

FIG. 85 illustrates an embodiment of a further aspect of the presentinvention. In this embodiment, the particle detection system 8500includes a transmitter 8502 and a receiver 8504. The transmitter 8502includes a light source or light sources adapted to emit light includinglight into wavelength bands λ₁ and λ₂. The light source 8502 can includea plurality of light emitting elements each adapted to emit in adifferent wavelength band, or a wide band light source. The transmitter8502 can additionally include one or more optical components e.g. 8506for forming a beam of light of desired beam profile or dispersioncharacteristics. The receiver 8504 can also include a light directing orimage forming optics 8508 which are adapted to form an image of the beamon a sensor array 8510 of the receiver 8504. In order to minimise theinterference of ambient light with the receiver 8504 the receiver 8504is also provided with a multiple passband filter arrangement 8512. Forexample, the multiple passband filter can be an interference filterwhich is arranged to selectively transmit light of the first passbandand second passband corresponding to emission bands of the light source8502. Most preferably, the filter arrangement 8512 is a multiplepassband interference filter which has a passband at a long wavelengthand one or more harmonics of that wavelength. In such an embodiment, thelight source 8502 must be configured to emit light at similarly relatedharmonics. For example, a single interference filter can be designed totransmit substantially all light at 800 nanometers and also at 400nanometers while blocking a large majority of light at otherwavelengths. When using such a filter the light source can be adapted toemit at 800 nanometers and 400 nanometers.

In a further embodiment of the present invention the filter arrangement8512 can include more than one interference filter or dye filter orother similar type of filter used in parallel. For example, two, or morefilters, corresponding to the number of wavelength bands in which thesystem is configured to operate, may be placed in side by siderelationship in the imaging path of the receiver. FIGS. 86 to 89illustrate examples of such filter arrangements. In this regard, thefilter arrangements of FIGS. 86 to 89 include portions adapted totransmit light in a first passband indicated by reference symbol 8602and shaded white, and alternate portions shaded grey and indicated withreference numeral 8604, which are adapted to transmit light in a secondpassband. FIG. 88 is adapted for use in a four wave length system andtherefore additionally includes portions indicated with referencenumeral 8606 and 8608 which are adapted to transmit light in a third andfourth wavelength bands. In each of the filter arrangements, the surfaceof the filter is approximately equally divided between the differentwavelength components and thus transmit substantially even amounts oflight in each wavelength band to the receiver. Such an arrangement has adisadvantage compared to the abovementioned multiple passband filterarrangement in that the effective receiver lens diameter is reduced e.g.by approximately one half for each wavelength in FIGS. 86, 87 and 89,thus reducing the effective signal strength. However this is to someextent compensated for by the fact that the light source LED need not beat harmonics of each other but can be selected on other merits such ascost of goods. Moreover, the filters used in such an arrangement may beof lower cost and not require such accurate wavelengths centring andtherefore will not be so sensitive to variations in transmitter outputwith temperature fluctuation.

FIG. 90 illustrates a schematic representation of a fire alarm system inwhich an embodiment of the present invention can be used. The fire alarmsystem 9000 includes a fire panel 9010 to which is connected a firealarm loop 9012. The fire alarm loop 9012 delivers power andcommunication from the fire panel to various pieces of fire alarmequipment attached to the system 9000. For example, the fire alarm loop9012 can be used to communicate with, and power, one or more pointdetectors 9014 and alarm sirens 9016. It can also be used to communicatewith one or more aspirated particle detectors such as detector 9018.Additionally, a beam detector system 9020 can also be attached to thefire alarm loop 9012. In the present invention the beam detector system9020 can be of the type described above in relation to any of theembodiments herein and include a receiver 9022 at a first end and at atransmitter 9024 located remotely to the receiver. Preferably, thetransmitter 9024 is a battery powered device and does not require powerto be drawn from the fire alarm loop 9012. Alternatively, it can bepowered e.g. off separate mains power or loop. The receiver 9022 isconnected to the fire alarm loop 9012 and draws power from the loop andcommunicates with the fire panel 9010 via the loop. The means ofcommunication will be known to those skilled in the art and allow thebeam detector 9020 to indicate a fire or fault condition or othercondition back to the fire panel 9010.

The present inventors have realised that since smoke detectors do notneed to respond instantaneously, acceptable average power consumptioncould be obtained by activating the video capture and/or videoprocessing subsystems of the smoke detector intermittently, interspersedwith periods when processing and capture is suspended. Thus the systemcan enter a “freeze” state in which it is designed to consume verylittle or no power.

A first way of achieving this solution is to provide the videoprocessing subsystem of the particle detector with a simple timer unitwhich operates to activate the video capture and processing subsystemsintermittently.

However, in the preferred form of the system the transmitter 9024 is notpowered from the loop or other mains power, but is battery powered andis preferably not connected to the receiver 9022 or in high speedcommunication with it. Consequently the transmitter 9024 must emit lightat only very low duty cycle to conserve power. In such a system thetiming of each transmitted burst of light may neither, be controlled bythe receiver or synchronised with any other receiver which may also becommunicating with the same transmitter 9022.

Furthermore, during the video processor “freeze” period the receiver9022 may still be required to manage other functions such as servicingpolls from the fire alarm loop, or blinking display LEDs or the like.Therefore, using a simple timer mechanism to activate the systemprocessor and awake it from its “freeze” state is not the preferredsolution to this problem.

In a preferred form of the present invention the receiver 9022 employs asecondary processor, having much lower power consumption than primaryprocessor, which is used to activate the primary processor and to dealwith other functions that must continue without interruption when theprimary processor is in its “freeze” state.

FIG. 91 illustrates a schematic block diagram of a receiver 9100embodying this aspect of the present invention.

The receiver 9100 includes an imaging chip 9102, e.g., a CMOS sensormanufactured by Aptina Inc, part number MT9V034, for receiving opticalsignals from a transmitter 9024.

It may optionally include an optical system 9104 e.g. a focusing lens,such as a standard 4.5 mm, f1.4 c-mount lens, for focusing the receivedelectro magnetic radiation onto the imaging chip in the desired manner.

The imaging chip 9102 is in data communication with a controller 9106which preferably is an Actel M1AGL600-V2 field programmable gate array(FPGA), and an associated memory 9108 including a PC28F256P33 flash ROMfor program storage, two IS61LV51216 high-speed RAMs for image storageand two CY621777DV30L RAMs for program execution and data storage. Thecontroller's function is to control the image chip 9102 and perform therequired sequence of data manipulations to carry out the functionsrequired by the detection system. The control means has sundryadditional components as required for correct operation as wellunderstood by those skilled in digital electronics design.

A second processor 9112 is also provided. This processor 9112 can be aTexas Instruments MSP430F2122 microcontroller or similar, and performsfunctions such as checking the health of the control means and if neededsignalling fault to external monitoring equipment if the control meansfails or if the control means, for any other reason, cannot perform itsrequired tasks. It is also responsible for the timely control of powerto the control and imaging means in order to minimize power consumption.This is performed by processor 9112 de-activating the main processor9106 when it is not needed and waking it up intermittently when it isrequired.

Processor 9112 is also in data communication with interface means 9114such as a display or user interface and is also connected to the firealarm loop to enable data communication with other equipment connectedto the fire alarm loop e.g. a fire panel.

In the preferred embodiment the interface 9114 means is used to notifyexternal monitoring equipment if an alarm or fault condition exists. Ifit is determined by the receiver that a fault exists, the interfacemeans notifies this to the monitoring equipment (e.g. fire panel 9010 ofFIG. 3) by opening a switch thereby interrupting the current flow out ofthe aforementioned monitoring equipment. In the preferred embodiment theswitch is a solid state arrangement employing MOSFET transistors whichhas the benefit of being activated and deactivated with very low powerconsumption. If it is determined by the receiver that an alarm conditionexists, the interface means notifies this to the monitoring equipment bydrawing current in excess of a predetermined threshold value from themonitoring equipment. In the preferred embodiment the excess currentdraw is achieved by the positioning of a bipolar-transistor,current-limited shunt across the interface wires from the monitoringequipment. A total current draw of approximately 50 mA is used to signalthe alarm condition. In the preferred embodiment, power for normaloperation is drawn from the connecting wires to the monitoring equipmentat a constant current of 3 mA under non-alarm conditions.

In the preferred embodiment of the present invention the transmitter9024 includes a controller to control its illumination pattern,illumination time, sequence and intensity for each of the light sources,e.g. infrared and ultra-violet. For example this could be a TexasInstruments MSP430F2122 microcontroller. The microcontroller alsodetects activation of the device when first installed. In the preferredembodiment of the transmitter, the power source is a Lithium ThionylChloride battery.

In a preferred form of the present invention, during commissioning ofthe system the main processor 9106 can be programmed to discover theillumination pattern of each of the light sources (eg light source 9024of FIG. 3) and over a period of preferably several minutes e.g. 10minutes, determine its activation pattern. This process can be repeatedfor all light sources associated with the receiver. The low powerprocessor 9112 can use the discovered light source sequencinginformation to activate the primary processor 9106 at the correct time.

As will be appreciated, by using a system of this structure the functionof the system which must operate at all times can be controlled by thevery low power consumption processor 9112 whilst the highly intensiveprocessing can be performed intermittently by the main video processor9106, and in doing so the average power can be maintained at arelatively low level.

The inventors have determined that, there are various and oftencompeting constraints associated with practical embodiments that must bedealt with when choosing the illumination pattern of the transmitter andcorresponding receiver operation to accurately acquire and track atransmitter output. For example, in some systems it is desirable to usethe rate of change of attenuation to distinguish fault conditions fromparticulate detection events. This complicates the use of longintegration times discussed in the background. The preferred embodimentuses an integration period of 10 seconds for normal measurements, and ashorter integration period of one second is used for rate of changebased fault detection.

Another constraint on system performance is the scene lighting level.For a practical system it is usually necessary to assume the scene maybe lit by sunlight for at least part of its operational life. There mayalso be limitations on the ability to use wavelength selective filterson the camera (e.g. at least cost limitations). Therefore. it will benecessary to use short exposures to avoid saturation, and still leavesufficient head room for the signal. In preferred implementations of thesystem the exposure duration is 100 μs, but the optimum value willdepend on the choice of sensor, filter, lens, worst case scene lightingand the amount of headroom required for the signal.

A means of synchronising the receiver with the transmitter is alsorequired. It is preferable to achieve this without the use of additionalhardware such as a radio system. Instead in one desirable implementationthe synchronisation is performed optically using the same imaging andprocessing hardware that is used for particle detection. However, as aperson skilled in the art will appreciate, the use of the same hardwarefor particle detection as for synchronisation links two concerns withinthe system, an thereby imposes a further constraint on the possiblesolutions.

Another constraint within the system is due to the presence of noise.The prime noise sources in the system are camera shot noise and noisefrom light variations in the scene. Dark noise is generally not asignificant contribution for systems that must deal with full sunlight.Scene noise is dealt with very effectively by the background subtractionmethod described in our earlier patent applications. Shot noise cannotbe totally removed, as it is fundamental to the quantum detectionprocess. However, shot noise can be reduced by reducing exposure time,and also by summing fewer exposures. In the preferred embodiment,substantially all transmitter power is put into very brief flashes, witha repetition rate that still allows an adequate system response time.

For example, a flash rate of 1 per second will satisfy the response timerequirement, and a flash duration of less than 1 μs and an exposure timeof 2 μs could (in principle) be used. In practice this would be verydifficult to synchronise. In addition, the transmitter LEDs would needto handle a very high peak current to deliver the energy in such a shorttime, which in turn would increase cost. Another limitation is thedynamic range of the sensor. Putting all the power into one flash persecond could result in saturation in the sensor.

In consideration of the above factors the preferred embodiment uses anexposure of 100 μs, a flash duration of 50 μs, and a period of 9000 ms.An integration length of 3 samples is used for rate of change basedfault detection. An integration length of 30 samples is used for smokemeasurements.

To perform the background cancellation techniques, the receiver alsoneeds to capture images just before and just after the flash that areused to eliminate the contribution from the scene. Ideally these “off”exposures would occur as close to the “on” exposure as possible tooptimise cancellation in the case of a time varying background. With thereceiver system used in the preferred implementation, the maximumpractical frame rate is 1000 fps, so the “off” exposures are spaced 1 mseither side of the “on” exposure.

In one form, the transmitter optical output consists of a series ofshort pulses, with a very low duty cycle. The pulses are placed to matchthe frame rate of the imaging system (e.g. 1000 fps). FIG. 92 shows anexemplary pulse sequence in relation to the sensor exposures in thereceiver. In this case the transmitter is adapted to emit light in an IRwavelength band and an μv wavelength band. This series of pulses isrepeated with a period of 9000 ms.

In the example, there are 5 pulses, as follows:

-   -   Sync 1 (frame 1) 110 and Sync 2 (frame 2) 112: Sync pulses are        used to maintain synchronisation (discussed more fully later)        between the transmitter and receiver. These are pulses are        preferably made in the wavelength band which is most power        efficient. In this case the IR light source is used because it        results in lower power consumption. Moreover the longer        wavelength is more able to penetrate smoke, so synchronisation        can be maintained in a greater range of conditions. The Sync        pulses are 50 μs long.    -   Ideally each synch pulse is centred in time on the leading (sync        1) and trailing edges (sync 2) of the receiver's shutter open        period. This makes their received intensity vary with small        synchronisation errors.    -   IR (frame 5) 114 and UV (frame 7) 116. The IR and UV pulses are        used for signal level measurement (and in turn used to measure        attenuation and smoke level.). They are 50 μs long, which allows        for up to 25 μs timing error between transmitter and receiver        without influencing the received intensity.    -   Data (frame 9) 118: The data pulse is used to transfer a small        amount of data to the receiver. The data is encoded by a either        transmitting or not transmitting the data pulse. The data pulse        has reduced amplitude to save power, and is IR for the same        reason. They are 50 μs long. This system provides a 3 bps data        channel. The data may include serial number, date of        manufacture, total running time, battery status and fault        conditions. Those skilled in the art would be aware of many        alternative ways to send data in this system. These could        include pulse position encoding, pulse width encoding, and multi        level encoding schemes. Greater data rates could readily be        achieved, however the simple scheme used in the preferred        implementation is sufficient for the small amount of data        needed.

In FIG. 92, the data from the receiver during “off” frames (i.e. frameswith no corresponding transmitter output) are used for the followingpurposes:

-   -   Frame 0 & 3 are used for background cancellation of the sync        pulses    -   Frame 4 & 6 are used for background cancellation of the IR pulse    -   Frame 6 & 8 are used for background cancellation of the UV pulse    -   Frame 8 & 10 are used for background cancellation of the Data        pulse    -   (a) Spatial Search

As described above, the receiver receives each of the transmitted pulsesin the form of one or more pixels within an image frame.

However, during commissioning when the system commences operation (atleast the first time) the locations of the transmitter(s) within theimage frame must be established. This could be performed for example, bya manual process involving an operator inspecting the image, andprogramming in the co-ordinates. However, the need for special training,special tools, and long complex installation processes for installationis undesirable. In the preferred embodiment determining the location ofthe transmitters within the image frame is automated. The preformedprocess for locating transmitters operates as follows:

-   -   The system first captures a number of images at a high frame        rate and for a time sufficient to ensure that transmitter        pulses, if the transmitter is within the field of view of the        camera and pulses are transmitted during the period of capture,        will be present in one or more images.    -   The system then subtracts each pair of (temporally) adjacent        images, and takes the modulus of each pixel and then tests each        against a threshold to detect locations of large variation, at        which a transmitter may be present.    -   The system then condenses the candidate list of transmitter        locations by merging candidate points that are adjacent or        nearby. (e.g. <3 pixels apart) A centre of gravity method can be        used to find the centre of a set of candidate points.    -   The system then performs a trial synchronisation (using the        process described below) at each of the candidate centres to        verify that the received value at a candidate centre corresponds        to a real transmitter.    -   The system then checks that the number of transmitters matches        the expected number of transmitters. This number may be set by        pre-programming the receiver prior to installation, or by a        switch or switches mounted on, in, or connected to the receiver        unit. In the preferred implementation, there is a set of        configuration DIP Switches incorporated into the receiver unit        and easily accessible only while the system is not mounted to        the wall.

The set of transmitter locations within the image is stored innon-volatile memory. The locations can be cleared by placing thereceiver into a particular mode, e.g. by setting the DIP switches to aparticular setting and powering/de-powering the receiver, or by the useof a special tool, such as a notebook PC. This is only required if atransmitter is moved from its original location or the system is to bere-installed elsewhere.

Performance limitations in the imaging system may limit the number ofpixels or lines that can be read out when operating at a high framerate. In one implementation, a maximum of 30 lines of 640 pixels can beread out in 1 ms. Therefore the first few steps of the above method needto be repeated 16 times to cover the entire 640*480 image frame.Alternatively, some embodiments employ only part of the image frame.Similarly, some embodiments use a slower frame rate. However, thepossibility of sensor saturation in bright lighting conditions generallylimits exposure time, and variations in background lighting conditionsgenerally introduce more noise if a lower frame rate is used.

The frame rate must be chosen to ensure that the transmitter pulses donot always occur in period where the shutter is closed. For example, ifthe frame rate is exactly 1000 fps, with an exposure of 100 us, and thetransmitter produces pulses on exact 1 ms boundaries, the pulses may allbe generated at times when the shutter is closed. The receiver framerate is chosen so that there is a slight difference causing a gradualphase shift, ensuring that sooner or later the pulses will fallsufficiently within a shutter open period.

In some embodiments, processing speed limitations are managed by notanalysing all of the pixels, instead only every nth (eg. 4th) horizontaland vertical pixel are subtracted and checked, reducing processingeffort (eg. by a factor of 16). Provided that the received image i.e.the image of each transmitter on the sensor, is spread over asufficiently larger area (e.g. a spot having a diameter of 5 pixels),then the transmitter will still be found reliably.

Whenever the system is powered up, either with a known set oftransmitter locations or as a part of the Spatial Search describedabove, with a set of candidate locations, a phase search and lock methodis used to establish initial synchronisation.

The major steps of this method are:

The system captures images at a high frame rate (at least a partialimage in the expected location).

The system waits for the expected pattern of pulses to appear at thecandidate centre locations.

The system uses the time of arrival of a selected pulse within theexpected pattern as a starting phase for the phase locked loop.

The system waits for stabilisation of the PLL. If no PLL lock is made,then in the case of testing candidate locations, the location is markedas spurious, otherwise when re-establishing synchronisation with a knowntransmitter location the receiver can re-try continually and assert afault until it is successful.

As with the spatial search, a small offset in the receiver frame rate isused to cause a gradual phase shift, ensuring that sooner or later thepulses will fall sufficiently within a shutter open period.

For each frame, the total intensity is calculated within a small regionof the image centred on the known or candidate location. This sequenceof intensity values is then checked for the expected pattern from thetransmitter.

The test for the expected pattern operates as follows:

After at least 9 frame intensity values have been collected, they can betested for the presence of the expected transmitter pulse sequence inthe following manner.

Given the intensity values I(n), 0<n<N,

Test for a possible transmitter signal starting with its frame 0 atframe n received

First, compute an “off frame” reference levelI ₀=(I _(R)(n+0)+I _(R)(n+3)+I _(R)(n+4)+I _(R)(n+6)+I _(R)(n+8))/5{mean of “off frames”}

Compute relative intensitiesI _(R)(n+m)=I(n+m)−I ₀ for m=0 to 8

Compare with pre-determined thresholds to determine the presence orabsence of a transmitter pulse in each frame

Found = {(I_(R)(n + 1) > I_(ON))  or   (I_(R)(n + 2) > I_(ON))}  and  {Sync 1  or  Sync 2  pulse}     (I_(R)(n + 5) > I_(ON))  and  {IR  pulse}     (I_(R)(n + 7) > I_(ON))  and  {UV  pulse}     (I_(R)(n + 0) < I_(OFF))  and  {off  frame}     (I_(R)(n + 3) < I_(OFF))  and  {off  frame}     (I_(R)(n + 4) < I_(OFF))  and  {off  frame}     (I_(R)(n + 6) < I_(OFF))  and  {off  frame}     (I_(R)(n + 8) < I_(OFF))  and  {off  frame}

Due to the random phase errors, either of the sync pulses may becompletely missing, hence the “or” in the above expression.Alternatively, the tests for the sync pulses can be omitted entirely,and the tests for the off frames can also be reduced. However, care mustbe taken to ensure that the position of the transmitter pulse sequenceis not falsely identified.

Following a positive detection, the time corresponding to the frame n isrecorded in a variable. The amplitudes of the phase pulses can be usedto trim the recorded time value to more closely represent the start ofthe sequence. This helps reduce the initial phase error that the phasedlocked loop has to deal with, and may not be required if frequencyerrors are sufficiently small.

In the preferred implementation the image capture rate 1000 fps whichmatches the transmitter timing as previously described. A shutter timeof 100 μs is used.

This completes the initial synchronisation. The arrival time of the nextset of pulses can now be predicted by simply adding the knowntransmitter period to the time recorded in the previous step.

Although the transmitter period is known to the receiver (300 ms in thepreferred implementation), there will be small errors in the clockfrequencies at each end. This will inevitably cause the transmittedpulses to become misaligned with the receiver shutter open time. A PhaseLocked Loop system is used to maintain the correct phase or timing. ThePLL concept is well known so will not be described in detail. In thepreferred implementation the PLL control equations are implemented insoftware. The Phase Comparator function is based on measuring theamplitude of the phase pulses. These amplitude are calculated bysubtracting the mean of the intensities measured in the nearest offframes (frames 0 & 3). The phase error is then computed with thefollowing formula:

$ɛ = {\frac{{I_{R}(1)} - {I_{R}(2)}}{2\left( {{I_{R}(1)} + {I_{R}(2)}} \right)} \cdot T}$where T is the width of the phase pulses.

In the case that the phase pulse amplitudes fall below a pre-determinedthreshold, the phase error is assigned a value of zero. This way noisydata is permitted into the PLL, and in practice the system is able tomaintain adequate synchronisation for at least a few minutes. Therefore,high smoke levels do not cause a synchronisation failure before an alarmcan be signalled. In the case of an obstruction, this feature allows thesystem to recover rapidly when the blockage is removed.

The PLL control equations include proportional and integral terms. Itwas not found necessary to use a differential term. In the preferredimplementation proportional gain and integrator gains of 0.3 and 0.01respectively were found to produce acceptable results. In a furthervariation, the gains can be set to larger values initially, and reducedafter the phase error is below a pre-determined threshold, thus reducingoverall lock time for a given loop bandwidth.

Phase error below +/−10 μs can be used to indicate phase lock, both forthe purpose of verifying a candidate transmitter location and also forallowing normal smoke detection operation to commence.

FIG. 93 illustrates an environmental monitoring system 9300 adapted tomonitor a region 9302 within a room 9304. The environmental monitoringsystem includes a beam detection subsystem 9306 which includes areceiver 9308 and four transmitters 9310, 9312, 9314, 9316. The beamdetection subsystem operates in accordance with an embodiment of any oneof the systems described above.

The environmental monitoring system 9300 additionally includes fouradditional environmental monitors 9318, 9320, 9322, 9324. Each of theadditional environmental monitors 9318 to 9324 may be of the same typebut alternatively each may be of a different type i.e. sense a differentenvironmental condition or the same condition by a different mechanism.The environmental monitors can include, for example, carbon dioxide,carbon monoxide, temperature, flame, other gas sensors or the like. Eachof the additional environmental monitors 9318 to 9324 is connected by acommunications channel to a nearby transmitter of the beam detectionsubsystem. For example, the additional environmental monitor 9318 isconnected via wire 9326 to corresponding transmitter 9310 of the beamdetection subsystem 9306. Similarly, environmental monitor 9320 is indata communication with transmitter 9312, environmental monitor 9322 isdata communication with transmitter 9314 and the environmental monitor9324 is in data communication with transmitter 9316. The datacommunications channel between each environmental monitor and itsrespective transmitter may be hard wired connection or may be via awireless connection e.g. radio, optical etc. communications link. Inmost embodiments the communications link need only be unidirectional,however it may in some embodiments be bidirectional. In theunidirectional case, the communications channel is adapted such that theenvironmental monitor can communicate an alarm and/or fault conditiondetected by it, or other output, e.g. a raw or processed sensor outputto the transmitter of the beam detection subsystem 9606.

As will be appreciated the environmental sensors can be housed withinthe transmitters rather than located remotely and connected by a longwire or communications link.

The transmitter of the beam detection subsystem 9306 is adapted toreceive signals from the environmental monitor and re-transmit these,with or without additional encoding, via an optical communicationschannel, back to the receiver 9308. The optical communications channelmay be implemented by modulating either the particle detection beam or asecondary beam transmitted by the transmitter to the receiver 9308. Thecommunications channel can be alternately or intermittently transmittedbetween pulses of the particle detection beam generated by thetransmitter. Alternatively, it may be continuously illuminated, possiblysimultaneously with a particle detection beam. In this case, thewavelength used for the particle detection beam or beams can bedifferent to that on which the optical communications channel isimplemented.

Using such a system, a network of environmental monitors may be placedaround the region being monitored 9302, and the environmental conditionssensed by these monitors can be communicated back to the receiver of thebeam detection subsystem. The receiver 9308 is in data communicationwith a fire alarm control panel e.g. via a fire alarm loop orproprietary network or other notification system without the need forcomplicated dedicated wiring system between the environmental monitornetwork and the fire alarm system. In a preferred embodiment, aplurality of optical communications channels can be differently encodedsuch that a receiver of the beam detection subsystem can distinguisheach optical communications channel from each other. For example, eachoptical communications channel may be modulated differently or may bescheduled to operate in a different time period. Thus effectively a timedivision multiplexing arrangement can be implemented for the differentoptical communications channels. Using different wavelengths for eachcommunications channel may also be possible.

The system also enables the location at which an environmental conditionis detected to be determined since the receiver 9308 can resolve opticalchannels from the different transmitters e.g. based on the signalreceived or where on the sensor the signal arrives if the receiverssensor is of a multi-sensor element type. The addressing information orchannel information can be passed to the fire alarm control panel andthe location of the alert be passed to an operator or fire authority.

In the example of FIG. 93 each of the transmitters and environmentalmonitors are preferably battery powered to remove any need for wiring.

FIG. 94 illustrates a further embodiment of this aspect of the presentinvention. In this embodiment, the environmental monitoring system 9400includes a beam detection subsystem 9402 as well as an environmentalmonitoring subsystem 9404. The beam detection subsystem includes areceiver 9406 and a transmitter 9408. The transmitter is adapted to emitone or more beams of light 9410 which are received by the receiver 9406.The receiver 9406 has a wide field of view having edges indicated bylines 9409, 9409B. Within the field of view of the receiver 9406 thereare positioned two environmental monitors 9412, 9414. Environmentalmonitors 9412 and 9414 may be of any of the types described above, andadditionally include a respective light emitter 9416, 9418. The lightemitters 9416, 9418 may be a low power LED or the like and are used togenerate an optical signal which is received by the receiver 9406. Eachof the LEDs 9416, 9418 can be individually modulated to communicate anoutput of the corresponding environmental monitors 9412, 9414 back tothe receiver 9406. As described in the previous embodiment, the opticalcommunications channels can be either time multiplexed or wavelengthmultiplexed with each other and with the particle detection beam orbeams 9410 emitted by the transmitter 9408. This embodiment has theadditional advantage over that of FIG. 93 that there is no need for anywiring or communications channel between the environmental monitors 9412and 9414 and the particle detection subsystem transmitter 9408.Accordingly installation costs are minimised.

FIG. 95 illustrates a component of a particle detector system. Thecomponent 9500 is a light source which is used to emit one or more beamsof light across a volume being monitored for particles. The light source9500 includes one or more light emitters 9502 which are connected tocircuitry 9504 which deliver power to the light emitters 9502. Theoperation of the light emitter 9502 is controlled by a microcontroller9506 which causes the light emitters to be illuminated in apredetermined fashion, e.g. to flash in a particular sequence. The lightsource 9500 is powered by a battery 9508. The output of the battery ismonitored by monitoring component 9510 and the environmental conditionsin which the component is operating are monitored by the environmentalmonitor 9512. The environmental monitor 9512 can be a temperaturesensing device such as a thermocouple. The controller 9506 receives theoutput of the battery monitor 9510 and the output of the environmentalsensor 9512 and determines an expected battery life.

More particularly, the controller receives signal representing thetemperature of the immediate surroundings of the battery and themeasured output voltage of the battery 9508. The battery output voltageis compared to a threshold voltage corresponding to the measuredtemperature and the discharge state of the battery 9508 is determined.

In an alternative embodiment, the battery monitor 9510 is adapted tomeasure the total current drawn from the battery. For example, themonitor 9510 can be an ammeter and determine the level of current beingdrawn from the battery. In this case, the controller is adapted tointegrate the measured current over time and the remaining availablecharge is determined. When the remaining charge available is calculatedto fall below the predetermined threshold an indication can be generatedof the impending discharged state of the battery.

In a further alternative, an estimate of the total current used can bemade. For example, in a preferred embodiment the majority of the chargedrawn from the battery will be drawn in pulses which are used forflashing the light emitters 9502. If the circuitry 9504 operates at aconstant current, which is preferred, the duration of operation of theLED multiplied by this constant current will provide a relativelyaccurate measurement of the total charge used by the system over time.In a cruder alternative the typical average current consumption known tobe required by the equipment can be pre-calculated and the length oftime of operation of the component can be used to determine the totalcurrent drawn from the battery over time.

In the above embodiments, the environmental conditions, mostadvantageously the temperature of the immediate surroundings of thebattery can be monitored over time and this temperature data can be usedby the controller to produce a more accurate estimate of the remainingcharge available in the battery 9808. As will be appreciated thecontroller can be adapted to calculate an estimate of the remainingbattery life available under the prevailing conditions. The remainingtime can be compared to a warning threshold and if the threshold isexceeded an indication of an approaching discharged state can begenerated.

In a preferred embodiment the predetermined time threshold at which anindication of an approaching discharged state of the battery will begenerated, may be selected in order to allow maintenance personnel toreceive an indication of the impending discharge of the battery during ascheduled maintenance event. If the warning of the impending dischargeof the battery can be given at a sufficiently early stage, say beforethe scheduled maintenance event prior to another scheduled maintenanceevent at which the battery will need to be changed then no extraunscheduled maintenance event will be required. Moreover, themaintenance personnel can ensure that the required equipment e.g.specialised tools and a battery is obtained prior to the maintenanceevent at which the battery will need to be changed. For example, where acomponent has a nominal battery life of 5 years and an annualmaintenance inspection is scheduled, an indication of impending batteryfailure can be raised say 13 or 14 months before the nominal end oflife. In this way at the inspection arising about 4 years aftercommissioning of the system the maintenance personnel will detect thatthe battery will need to be changed at the following maintenance session(in a year's time) and can plan to bring a replacement battery on thenext annual visit. It should be understood that to avoid failure of thesystem the nominal battery life is set with a significant safety margin.The time of 13 or 14 months is chosen to allow a scheduling margin forthe two maintenance sessions i.e. the one at which the maintenancepersonnel learns of the battery discharge state, and the next one atwhich it will be changed.

In a preferred form of the present invention, when the component beingmonitored is a light source of the particle detector, the light sourcecontroller can be adapted to signal the battery state to the receiver.This can be done by modulating the amplitude, duration and/or timing ofone or more transmitted light pulses in a predetermined fashion. Thelight pulse used for data transmission can be one of the light pulsesused in particle detection or an additional light pulse added to thesequence of light pulses produced by the light source for the purposesof data communication from the light source to the receiver. Asdescribed above, such a scheme avoids the need for wiring between theunits. Alternatively, the light source may be fitted with additional lowpowered LED which can be flashed to indicate to a person (rather thanthe receiver) located remotely from it, the state of its battery.

In a particularly sophisticated embodiment, the controller of the lightsource can be adapted to generate a battery output signal e.g. bymodulating a light beam in a particular code, with which indicates atime until expected a battery discharge. For example, the output signalcan indicate the number of months until the battery is expected to beflat. This allows the maintenance personnel to more accurately schedulethe next scheduled maintenance session, and also determine if thebattery will need to be replaced before the next scheduled visit.Moreover if an accurate ‘time to full discharge’ is known then the lightsource can go into a low power mode e.g. in which its duty cycle isreduced from normal to extend battery life. The receiver can beprogrammed to detect this low duty cycle mode and indicate a fault if alow duty cycle modulation patterns is observed.

FIG. 96 illustrates a system according to a further embodiment of thepresent invention. In this system 9600 there is provided a firstreceiver 9602 which is associated with a pair of transmitters 9604 and9608. The first transmitter 9604 transmits a first beam of light 9606,and the second transmitter 9608 transmits corresponding beam of light9610. Both beams of light are received by the receiver 9602 and particledetection decisions can be made in accordance with embodiments of theinvention described herein. The system 9600 additionally includes areceiver 9612 and associated transmitter 9614 which transmits a beam oflight 9616. The beam 9616 is received by the receiver 9612 which can beadapted to determine the presence of particles as described elsewhereherein. The beam detector arrangement effectively provides three beamdetectors that have beams that are coincident (or practicallycoincident) at two places. Both of the receivers 9602 and 9612 areconnected to a controller 9618 which is adapted to apply fault and/oralarm logic to determine that the fault conditions and/or particledetection conditions exist. As will be appreciated, the intersectingbeams 9606 and 9616, and 9610 and 9616 enable the system 9600 todetermine whether particles have been detected at the points ofintersection of the beams by correlations the outputs from the receivers9602 and 9612. Such an arrangement also enables relatively advancedprocessing to be implemented and enables the particle detectionalgorithms of each of the individual beam detectors to differ from thatused in a single stand alone beam detector. For example, a simple doubleknock system can be implemented in which at least two of the beams mustdetect particles above a predetermined threshold level before an alarmis raised. In a preferred form such a system may reduce overall falsealarm rates as a false alarm condition is unlikely to occur in twodifferent beams. However, this also permits a lower alarm threshold tobe used, thus enabling faster detection of particles, withoutsubstantially affecting the false alarm rate of the system. In such asystem, the false alarm probability of the entire system is the same asthe product of the individual false alarm probabilities of the beams. Aswill be appreciated, both of the advantages of the above systems can beobtained to some extent by setting an alarm threshold which compromisesbetween sensitivity and false alarm rate improvement. Moreover, temporalcharacteristics of the particle detection outputs of the various beamdetectors can be used to improve particle detection performance orreduce false alarm occurrences. In this regard, the time separationbetween occurrences of suspected smoke events in each of the beams canbe used to improve probability of early detection without increasingfalse alarm. For example, the time which each of a pair of substantiallycoincident beams goes into alarm, can be used to determine whether thealarm condition is caused by the presence of particles or a false alarm.If they are substantially coincident in time then the particle detectionevent is likely to be genuine. On the other hand, if the particledetection event occurs at substantially different times in each of thebeams then this is likely to indicate a false alarm is present. Insophisticated systems it may be possible to compare time varyingparticle detection profiles from each of the beam detectors to identifycorresponding particle detection events. For example, this could be doneby cross correlating the outputs of a plurality of substantiallycoincident beam detectors within the system. In the event that highcross correlation between a pair of outputs is determined this canindicate that the output of each of the beam detectors are bothexperiencing similar conditions e.g. the same particle detection eventor same false alarm event. A determination as to which type of event itis could be made by analysing the profiles e.g. a duration ofobscuration; a level of obscuration; rate of change at the outset ofobservation etc to determine if the event is caused by the presence ofparticles or a foreign body.

It will be understood that the invention disclosed and defined in thisspecification extends to all alternative combinations of two or more ofthe individual features mentioned or evident from the text or drawings.All of these different combinations constitute various alternativeaspects of the invention.

What is claimed is:
 1. A particle detector component; the componentincluding a mounting portion, an optical module, and locking means; themounting portion being fixedly attachable to a mounting surface; theoptical module including one or more light sources and/or one or morelight receivers to enable detection of particles based at least partlyon non-visible light, the optical module being articulated relative tothe mounting portion for alignment relative to a target and includingmeans for enabling a visual indication of said alignment; and thelocking means being actuatable to lock the optical module relative tothe mounting portion in a selected alignment, wherein the means forenabling a visual indication is an engagement feature for cooperatingwith a visual alignment tool, the visual alignment tool incorporating avisual targeting means that includes an electro-optical device, whereinthe locking means is actuatable by the visual alignment tool via themeans for enabling a visual indication of said alignment.
 2. Theparticle detector component as claimed in claim 1 wherein the means forenabling a visual indication is the visual targeting means.
 3. Theparticle detector component as claimed in claim 1 wherein the opticalmodule includes an elongate recess forming the engagement feature. 4.The particle detector component as claimed in claim 3 wherein the recesshas at least one open end and is arranged so that the axis of the recessprojects toward the target when the optical module is in alignment withit.
 5. The particle detector component as claimed in claim 3 wherein therecess projects in any one of: a direction parallel to a limit of afield of operation of the optical module; or any known physicalrelationship with the spatial optical characteristics of the opticalmodule.
 6. The particle detector component as claimed in claim 3 whereinthe locking means includes a driven member located within the recess andengageable with a driver of the visual alignment tool to actuate thelocking means.
 7. The particle detector component as claimed in claim 6wherein the locking means is adapted to be rotationally driven about theaxis of the recess to a selected orientation to actuate the lockingmeans.
 8. The particle detector component as claimed in claim 1 whereinone of the optical module and the mounting portion, is captured withinthe other portion, said articulation being effected by a sphericalsliding fit between the optical module and the mounting portion.
 9. Theparticle detector component as claimed in claim 6 wherein the drivenmember is a grub screw within one of the optical module and mountingportion, and rotatable to engage the other of the optical module ormounting portion.
 10. The particle detector component as claimed inclaim 6 wherein the optical module includes a brake shoe and a cam,wherein the cam is arranged to be driven by the driven member and inturn drive the brake shoe to, frictionally or otherwise, engage themounting portion and thereby lock the optical module relative to themounting portion.
 11. The particle detector component as claimed inclaim 10 wherein the cam is attached to the driven member or integrallyformed therewith.
 12. The particle detector component as claimed inclaim 10 wherein the braking shoe is biased towards a retracted,non-braking, position.
 13. The particle detector component as claimed inclaim 1 wherein the optical module includes any one or more of thefollowing: a lens; a mirror for redirecting a beam; a light emittingelement; and light receiver.
 14. The particle detector component asclaimed in claim 1 wherein the particle detector component is configuredto operatively connect a circuit, to enable operation of anelectro-optical element, to a power supply when said locking means isactuated.
 15. The particle detector component as claimed in claim 6wherein a switch may be associated with the driven member.
 16. Theparticle detector component as claimed in claim 15 wherein the drivenmember caries, at a point at a radius from its axis a magnet which isarranged to act on a reed switch when the driven member is rotated to aselected orientation.
 17. A component of a smoke detector comprising: anoptical module including one or more light sources and/or one or morelight receivers to enable detection of smoke based at least partly onnon-visible light; mounting means for mounting the optical module to asupport surface; an articulated connection located between the mountingmeans and the optical module; and a visual alignment device fixed tomove with the optical module for assisting in aligning the light sourceor sources and/or receiver or receivers, relative to a target, whereinthe articulated connection includes one or more locking means forlocking the orientation of the optical module relative to the mountingmeans, wherein the locking means comprises a driven member that isaccessible via the visual alignment device.
 18. The component of a smokedetector as claimed in claim 17 wherein the visual alignment devicecomprises one or more sockets in the optical module in which analignment beam generator can be inserted.
 19. The component of a smokedetector as claimed claim 17 wherein the articulated connectioncomprises a ball and cup joint, capable of allowing the optical moduleto be tilted relative to the mounting means through a relatively largearc of tilt, the locking means adapted to lock the ball to the cup in aselected orientation.
 20. The component of a smoke detector as claimedin claim 19 wherein the driven member is a screw member which engages ina threaded bore in the cup and contacts the surface of the ball to lockthe ball and cup together.
 21. The component of a smoke detector asclaimed in claim 17 wherein the locking means is configured tooperatively connect a circuit, to enable operation of an electro-opticalelement, to a power supply when said locking means is actuated.
 22. Thecomponent of a smoke detector as claimed in claim 17 wherein the visualalignment device comprises a laser housed in or mounted on a cylindricaltube or shaft sized to be a sliding fit in a socket of said one or moresockets.
 23. The component of a smoke detector as claimed in claim 22wherein the laser forms part of a tool having a driver at one end of thetool for locking the articulated connection.
 24. The component of asmoke detector as claimed in claim 17 wherein the component is any oneof a transmitter, receiver or target for a particle detector.
 25. Avisual alignment tool having: engagement means for engaging with andaligning the visual alignment tool relative to a particle detectorcomponent; and visual targeting means for providing a visual indicationof the alignment of the particle detector component when so engaged,wherein the visual alignment tool includes a driver for engaging withand actuating a locking means of a particle detector component.
 26. Thevisual alignment tool as claimed in claim 25 wherein the visualtargeting means is a camera.
 27. The visual alignment tool as claimed in25 wherein the visual targeting means is a means for projecting avisible light beam.
 28. The visual alignment tool as claimed in claim 25wherein visual alignment tool includes an elongate handle and a shaft,the shaft projecting from an end of the handle and being coaxiallyaligned therewith, wherein at least a portion of the shaft forms theengagement means.
 29. The visual alignment tool as claimed in claim 25wherein the visual alignment tool includes a driver for engaging withand actuating a locking means of a particle detector component.
 30. Thevisual alignment tool as claimed in claim 29 wherein the driver isformed at an end of the shaft distal from the handle and rotatable aboutthe axis of the shaft to actuate the locking means.
 31. The visualalignment tool as claimed in claim 29 wherein the driver is selectedfrom a list including: an allen key (hex); phillips head; and otherproprietary shaped driver.
 32. A particle detector including: acomponent including a mounting portion, an optical module, and lockingmeans; the mounting portion being fixedly attachable to a mountingsurface; the optical module being articulated relative to the mountingportion for alignment relative to a target and including means forenabling a visual indication of said alignment; and the locking meansbeing actuatable to lock the optical module relative to the mountingportion in a selected alignment; wherein the means for enabling a visualindication is an engagement feature for cooperating with a visualalignment tool, the visual alignment tool incorporating a visualtargeting means that includes an electro-optical device, wherein thelocking means is actuatable by the visual alignment tool, via the meansfor enabling a visual indication of said alignment.
 33. A particledetector according to claim 32, wherein the optical module includes anelongate recess forming the engagement feature.
 34. A particle detectoraccording to claim 32, wherein the particle detector is a smoke detectorthat detects particles based at least partly on non-visible light.
 35. Aparticle detector according to claim 34 wherein the detection is basedon any one of: at least ultraviolet light; at least infrared light; orultraviolet and infrared light.